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 $181.92   11.703%   $203.2101   $203.21   $203.20   $203.20  
  Purchase #2 $67.69   5.384%   $71.3344   $71.33   $71.35   $71.30  
  Purchase #3 $210.74   3.352%   $217.804   $217.80   $217.80   $217.80  
  Purchase #4 $48.97   4.215%   $51.0341   $51.03   $51.05   $51.00  
  Purchase #5 $226.85   4.472%   $236.9947   $236.99   $237.00   $237.00  
  Purchase #6 $64.37   11.776%   $71.9502   $71.95   $71.95   $72.00  
  Purchase #7 $84.37   6.235%   $89.6305   $89.63   $89.65   $89.60  
  7 purchase totals = $884.91       $941.9580   $941.94   $942.00   $941.90