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 $232.65   7.137%   $249.2542   $249.25   $249.25   $249.30  
  Purchase #2 $133.72   5.191%   $140.6614   $140.66   $140.65   $140.70  
  Purchase #3 $56.56   9.244%   $61.7884   $61.79   $61.80   $61.80  
  Purchase #4 $210.28   12.293%   $236.1297   $236.13   $236.15   $236.10  
  Purchase #5 $159.66   5.705%   $168.7686   $168.77   $168.75   $168.80  
  Purchase #6 $85.44   10.499%   $94.4103   $94.41   $94.40   $94.40  
  Purchase #7 $9.32   13.817%   $10.6077   $10.61   $10.60   $10.60  
  7 purchase totals = $887.63       $961.6203   $961.62   $961.60   $961.70