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 $59.90   3.518%   $62.0073   $62.01   $62.00   $62.00  
  Purchase #2 $62.58   10.271%   $69.0076   $69.01   $69.00   $69.00  
  Purchase #3 $5.65   6.803%   $6.0344   $6.03   $6.05   $6.00  
  Purchase #4 $22.51   6.708%   $24.02   $24.02   $24.00   $24.00  
  Purchase #5 $244.95   11.843%   $273.9594   $273.96   $273.95   $274.00  
  Purchase #6 $159.90   8.277%   $173.1349   $173.13   $173.15   $173.10  
  Purchase #7 $9.75   4.159%   $10.1555   $10.16   $10.15   $10.20  
  7 purchase totals = $565.24       $618.3191   $618.32   $618.30   $618.30