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 $53.28   13.610%   $60.5314   $60.53   $60.55   $60.50  
  Purchase #2 $162.89   4.593%   $170.3715   $170.37   $170.35   $170.40  
  Purchase #3 $202.98   6.716%   $216.6121   $216.61   $216.60   $216.60  
  Purchase #4 $159.93   8.368%   $173.3129   $173.31   $173.30   $173.30  
  Purchase #5 $99.66   8.601%   $108.2318   $108.23   $108.25   $108.20  
  Purchase #6 $72.37   9.592%   $79.3117   $79.31   $79.30   $79.30  
  Purchase #7 $201.63   6.637%   $215.0122   $215.01   $215.00   $215.00  
  7 purchase totals = $952.74       $1,023.3836   $1,023.37   $1,023.35   $1,023.30