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 $104.61   11.155%   $116.2792   $116.28   $116.30   $116.30  
  Purchase #2 $250.54   3.356%   $258.9481   $258.95   $258.95   $258.90  
  Purchase #3 $5.30   9.316%   $5.7937   $5.79   $5.80   $5.80  
  Purchase #4 $127.33   4.511%   $133.0739   $133.07   $133.05   $133.10  
  Purchase #5 $175.51   3.563%   $181.7634   $181.76   $181.75   $181.80  
  Purchase #6 $11.59   10.431%   $12.799   $12.80   $12.80   $12.80  
  Purchase #7 $247.56   5.642%   $261.5273   $261.53   $261.55   $261.50  
  7 purchase totals = $922.44       $970.1846   $970.18   $970.20   $970.20