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 $78.26   6.636%   $83.4533   $83.45   $83.45   $83.50  
  Purchase #2 $245.61   8.736%   $267.0665   $267.07   $267.05   $267.10  
  Purchase #3 $92.91   6.575%   $99.0188   $99.02   $99.00   $99.00  
  Purchase #4 $207.96   13.713%   $236.4776   $236.48   $236.50   $236.50  
  Purchase #5 $193.45   6.456%   $205.9391   $205.94   $205.95   $205.90  
  Purchase #6 $104.51   13.140%   $118.2426   $118.24   $118.25   $118.20  
  Purchase #7 $21.87   7.147%   $23.433   $23.43   $23.45   $23.40  
  7 purchase totals = $944.57       $1,033.6309   $1,033.63   $1,033.65   $1,033.60