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 $65.41   4.763%   $68.5255   $68.53   $68.55   $68.50  
  Purchase #2 $94.58   4.718%   $99.0423   $99.04   $99.05   $99.00  
  Purchase #3 $44.93   6.650%   $47.9178   $47.92   $47.90   $47.90  
  Purchase #4 $227.90   8.202%   $246.5924   $246.59   $246.60   $246.60  
  Purchase #5 $49.90   4.113%   $51.9524   $51.95   $51.95   $52.00  
  Purchase #6 $73.51   7.802%   $79.2453   $79.25   $79.25   $79.20  
  Purchase #7 $96.27   11.824%   $107.653   $107.65   $107.65   $107.70  
  7 purchase totals = $652.50       $700.9287   $700.93   $700.95   $700.90