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 $209.68   12.162%   $235.1813   $235.18   $235.20   $235.20  
  Purchase #2 $207.55   7.397%   $222.9025   $222.90   $222.90   $222.90  
  Purchase #3 $64.69   9.746%   $70.9947   $70.99   $71.00   $71.00  
  Purchase #4 $143.49   6.265%   $152.4796   $152.48   $152.50   $152.50  
  Purchase #5 $48.46   4.229%   $50.5094   $50.51   $50.50   $50.50  
  Purchase #6 $118.78   6.396%   $126.3772   $126.38   $126.40   $126.40  
  Purchase #7 $193.39   11.142%   $214.9375   $214.94   $214.95   $214.90  
  7 purchase totals = $986.04       $1,073.3822   $1,073.38   $1,073.45   $1,073.40