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 $92.25   9.692%   $101.1909   $101.19   $101.20   $101.20  
  Purchase #2 $195.93   7.526%   $210.6757   $210.68   $210.70   $210.70  
  Purchase #3 $238.61   4.577%   $249.5312   $249.53   $249.55   $249.50  
  Purchase #4 $36.98   7.190%   $39.6389   $39.64   $39.65   $39.60  
  Purchase #5 $78.42   8.729%   $85.2653   $85.27   $85.25   $85.30  
  Purchase #6 $166.38   11.321%   $185.2159   $185.22   $185.20   $185.20  
  Purchase #7 $61.30   8.320%   $66.4002   $66.40   $66.40   $66.40  
  7 purchase totals = $869.87       $937.9181   $937.93   $937.95   $937.90