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 $39.55   8.841%   $43.0466   $43.05   $43.05   $43.00  
  Purchase #2 $96.95   11.424%   $108.0256   $108.03   $108.05   $108.00  
  Purchase #3 $104.81   12.140%   $117.5339   $117.53   $117.55   $117.50  
  Purchase #4 $239.75   4.738%   $251.1094   $251.11   $251.10   $251.10  
  Purchase #5 $209.67   3.572%   $217.1594   $217.16   $217.15   $217.20  
  Purchase #6 $40.58   8.553%   $44.0508   $44.05   $44.05   $44.10  
  Purchase #7 $126.36   9.502%   $138.3667   $138.37   $138.35   $138.40  
  7 purchase totals = $857.67       $919.2924   $919.30   $919.30   $919.30