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 $249.68   10.439%   $275.7441   $275.74   $275.75   $275.70  
  Purchase #2 $205.86   11.226%   $228.9698   $228.97   $228.95   $229.00  
  Purchase #3 $152.54   13.221%   $172.7073   $172.71   $172.70   $172.70  
  Purchase #4 $34.67   13.245%   $39.262   $39.26   $39.25   $39.30  
  Purchase #5 $242.72   7.846%   $261.7638   $261.76   $261.75   $261.80  
  Purchase #6 $166.56   7.178%   $178.5157   $178.52   $178.50   $178.50  
  Purchase #7 $32.40   12.678%   $36.5077   $36.51   $36.50   $36.50  
  7 purchase totals = $1,084.43       $1,193.4704   $1,193.47   $1,193.40   $1,193.50