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 $67.89   12.677%   $76.4964   $76.50   $76.50   $76.50  
  Purchase #2 $207.76   3.846%   $215.7504   $215.75   $215.75   $215.80  
  Purchase #3 $64.46   4.354%   $67.2666   $67.27   $67.25   $67.30  
  Purchase #4 $246.39   12.786%   $277.8934   $277.89   $277.90   $277.90  
  Purchase #5 $249.56   4.321%   $260.3435   $260.34   $260.35   $260.30  
  Purchase #6 $68.73   8.668%   $74.6875   $74.69   $74.70   $74.70  
  Purchase #7 $21.28   13.180%   $24.0847   $24.08   $24.10   $24.10  
  7 purchase totals = $926.07       $996.5225   $996.52   $996.55   $996.60