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 $53.54   8.864%   $58.2858   $58.29   $58.30   $58.30  
  Purchase #2 $245.96   6.474%   $261.8835   $261.88   $261.90   $261.90  
  Purchase #3 $95.70   4.308%   $99.8228   $99.82   $99.80   $99.80  
  Purchase #4 $112.35   8.317%   $121.6941   $121.69   $121.70   $121.70  
  Purchase #5 $244.49   12.837%   $275.8752   $275.88   $275.90   $275.90  
  Purchase #6 $159.26   5.763%   $168.4382   $168.44   $168.45   $168.40  
  Purchase #7 $178.54   13.527%   $202.6911   $202.69   $202.70   $202.70  
  7 purchase totals = $1,089.84       $1,188.6907   $1,188.69   $1,188.75   $1,188.70