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 $186.79   7.863%   $201.4773   $201.48   $201.50   $201.50  
  Purchase #2 $189.73   9.254%   $207.2876   $207.29   $207.30   $207.30  
  Purchase #3 $92.76   11.713%   $103.625   $103.63   $103.65   $103.60  
  Purchase #4 $110.27   11.363%   $122.8   $122.80   $122.80   $122.80  
  Purchase #5 $47.38   10.453%   $52.3326   $52.33   $52.35   $52.30  
  Purchase #6 $199.32   3.185%   $205.6683   $205.67   $205.65   $205.70  
  Purchase #7 $37.90   4.223%   $39.5005   $39.50   $39.50   $39.50  
  7 purchase totals = $864.15       $932.6913   $932.70   $932.75   $932.70