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 $204.68   13.339%   $231.9823   $231.98   $232.00   $232.00  
  Purchase #2 $128.45   11.500%   $143.2218   $143.22   $143.20   $143.20  
  Purchase #3 $48.84   12.322%   $54.8581   $54.86   $54.85   $54.90  
  Purchase #4 $112.79   6.155%   $119.7322   $119.73   $119.75   $119.70  
  Purchase #5 $123.97   8.479%   $134.4814   $134.48   $134.50   $134.50  
  Purchase #6 $101.98   4.853%   $106.9291   $106.93   $106.95   $106.90  
  Purchase #7 $133.75   13.458%   $151.7501   $151.75   $151.75   $151.80  
  7 purchase totals = $854.46       $942.9550   $942.95   $943.00   $943.00