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 $54.47   6.286%   $57.894   $57.89   $57.90   $57.90  
  Purchase #2 $149.88   12.458%   $168.5521   $168.55   $168.55   $168.60  
  Purchase #3 $201.50   4.166%   $209.8945   $209.89   $209.90   $209.90  
  Purchase #4 $63.83   3.415%   $66.0098   $66.01   $66.00   $66.00  
  Purchase #5 $226.34   13.717%   $257.3871   $257.39   $257.40   $257.40  
  Purchase #6 $228.99   13.847%   $260.6982   $260.70   $260.70   $260.70  
  Purchase #7 $236.66   3.503%   $244.9502   $244.95   $244.95   $245.00  
  7 purchase totals = $1,161.67       $1,265.3859   $1,265.38   $1,265.40   $1,265.50