Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $179.78   8.793%   $195.5881   $195.59   $195.60   $195.60  
  Purchase #2 $231.30   9.718%   $253.7777   $253.78   $253.80   $253.80  
  Purchase #3 $96.51   11.222%   $107.3404   $107.34   $107.35   $107.30  
  Purchase #4 $235.88   13.864%   $268.5824   $268.58   $268.60   $268.60  
  Purchase #5 $129.98   12.844%   $146.6746   $146.67   $146.65   $146.70  
  Purchase #6 $208.33   10.446%   $230.0922   $230.09   $230.10   $230.10  
  Purchase #7 $126.72   11.153%   $140.8531   $140.85   $140.85   $140.90  
  7 purchase totals = $1,208.50       $1,342.9085   $1,342.90   $1,342.95   $1,343.00