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 $189.46   6.236%   $201.2747   $201.27   $201.25   $201.30  
  Purchase #2 $95.63   7.518%   $102.8195   $102.82   $102.80   $102.80  
  Purchase #3 $118.56   8.778%   $128.9672   $128.97   $128.95   $129.00  
  Purchase #4 $129.25   9.800%   $141.9165   $141.92   $141.90   $141.90  
  Purchase #5 $168.92   5.226%   $177.7478   $177.75   $177.75   $177.70  
  Purchase #6 $124.95   11.166%   $138.9019   $138.90   $138.90   $138.90  
  Purchase #7 $142.97   5.103%   $150.2658   $150.27   $150.25   $150.30  
  7 purchase totals = $969.74       $1,041.8934   $1,041.90   $1,041.80   $1,041.90