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 $31.90   3.277%   $32.9454   $32.95   $32.95   $32.90  
  Purchase #2 $235.30   9.560%   $257.7947   $257.79   $257.80   $257.80  
  Purchase #3 $78.55   9.106%   $85.7028   $85.70   $85.70   $85.70  
  Purchase #4 $49.66   7.601%   $53.4347   $53.43   $53.45   $53.40  
  Purchase #5 $94.29   3.220%   $97.3261   $97.33   $97.35   $97.30  
  Purchase #6 $144.51   3.367%   $149.3757   $149.38   $149.40   $149.40  
  Purchase #7 $60.86   6.416%   $64.7648   $64.76   $64.75   $64.80  
  7 purchase totals = $695.07       $741.3442   $741.34   $741.40   $741.30