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 $222.79   5.489%   $235.0189   $235.02   $235.00   $235.00  
  Purchase #2 $178.69   9.312%   $195.3296   $195.33   $195.35   $195.30  
  Purchase #3 $166.59   12.340%   $187.1472   $187.15   $187.15   $187.10  
  Purchase #4 $149.83   8.134%   $162.0172   $162.02   $162.00   $162.00  
  Purchase #5 $141.53   3.361%   $146.2868   $146.29   $146.30   $146.30  
  Purchase #6 $42.38   6.110%   $44.9694   $44.97   $44.95   $45.00  
  Purchase #7 $22.90   9.106%   $24.9853   $24.99   $25.00   $25.00  
  7 purchase totals = $924.71       $995.7544   $995.77   $995.75   $995.70