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 $82.81   12.237%   $92.9435   $92.94   $92.95   $92.90  
  Purchase #2 $206.51   7.383%   $221.7566   $221.76   $221.75   $221.80  
  Purchase #3 $245.66   4.708%   $257.2257   $257.23   $257.25   $257.20  
  Purchase #4 $42.45   9.327%   $46.4093   $46.41   $46.40   $46.40  
  Purchase #5 $239.56   6.340%   $254.7481   $254.75   $254.75   $254.70  
  Purchase #6 $50.69   11.580%   $56.5599   $56.56   $56.55   $56.60  
  Purchase #7 $21.63   11.488%   $24.1149   $24.11   $24.10   $24.10  
  7 purchase totals = $889.31       $953.7580   $953.76   $953.75   $953.70