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 $58.90   6.630%   $62.8051   $62.81   $62.80   $62.80  
  Purchase #2 $190.40   10.263%   $209.9408   $209.94   $209.95   $209.90  
  Purchase #3 $119.32   5.851%   $126.3014   $126.30   $126.30   $126.30  
  Purchase #4 $95.85   7.661%   $103.1931   $103.19   $103.20   $103.20  
  Purchase #5 $238.78   13.188%   $270.2703   $270.27   $270.25   $270.30  
  Purchase #6 $50.81   6.314%   $54.0181   $54.02   $54.00   $54.00  
  Purchase #7 $178.69   8.633%   $194.1163   $194.12   $194.10   $194.10  
  7 purchase totals = $932.75       $1,020.6451   $1,020.65   $1,020.60   $1,020.60