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 $245.93   3.767%   $255.1942   $255.19   $255.20   $255.20  
  Purchase #2 $22.81   11.838%   $25.5102   $25.51   $25.50   $25.50  
  Purchase #3 $181.81   6.642%   $193.8858   $193.89   $193.90   $193.90  
  Purchase #4 $59.25   7.817%   $63.8816   $63.88   $63.90   $63.90  
  Purchase #5 $102.90   4.774%   $107.8124   $107.81   $107.80   $107.80  
  Purchase #6 $62.27   11.209%   $69.2498   $69.25   $69.25   $69.20  
  Purchase #7 $197.99   7.289%   $212.4215   $212.42   $212.40   $212.40  
  7 purchase totals = $872.96       $927.9555   $927.95   $927.95   $927.90