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 $52.55   11.428%   $58.5554   $58.56   $58.55   $58.60  
  Purchase #2 $187.98   11.706%   $209.9849   $209.98   $210.00   $210.00  
  Purchase #3 $246.77   8.458%   $267.6418   $267.64   $267.65   $267.60  
  Purchase #4 $25.54   3.182%   $26.3527   $26.35   $26.35   $26.40  
  Purchase #5 $158.71   10.597%   $175.5285   $175.53   $175.55   $175.50  
  Purchase #6 $128.59   4.640%   $134.5566   $134.56   $134.55   $134.60  
  Purchase #7 $124.78   5.752%   $131.9573   $131.96   $131.95   $132.00  
  7 purchase totals = $924.92       $1,004.5772   $1,004.58   $1,004.60   $1,004.70