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 $136.66   3.329%   $141.2094   $141.21   $141.20   $141.20  
  Purchase #2 $83.37   10.702%   $92.2923   $92.29   $92.30   $92.30  
  Purchase #3 $17.37   11.790%   $19.4179   $19.42   $19.40   $19.40  
  Purchase #4 $197.45   3.204%   $203.7763   $203.78   $203.80   $203.80  
  Purchase #5 $180.99   9.674%   $198.499   $198.50   $198.50   $198.50  
  Purchase #6 $197.43   12.185%   $221.4868   $221.49   $221.50   $221.50  
  Purchase #7 $71.69   7.312%   $76.932   $76.93   $76.95   $76.90  
  7 purchase totals = $884.96       $953.6137   $953.62   $953.65   $953.60