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 $87.54   8.428%   $94.9179   $94.92   $94.90   $94.90  
  Purchase #2 $222.67   12.860%   $251.3054   $251.31   $251.30   $251.30  
  Purchase #3 $215.77   6.824%   $230.4941   $230.49   $230.50   $230.50  
  Purchase #4 $150.66   3.126%   $155.3696   $155.37   $155.35   $155.40  
  Purchase #5 $212.80   5.649%   $224.8211   $224.82   $224.80   $224.80  
  Purchase #6 $81.66   9.753%   $89.6243   $89.62   $89.60   $89.60  
  Purchase #7 $112.77   7.322%   $121.027   $121.03   $121.05   $121.00  
  7 purchase totals = $1,083.87       $1,167.5594   $1,167.56   $1,167.50   $1,167.50