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 $53.96   11.698%   $60.2722   $60.27   $60.25   $60.30  
  Purchase #2 $239.52   12.148%   $268.6169   $268.62   $268.60   $268.60  
  Purchase #3 $234.55   6.328%   $249.3923   $249.39   $249.40   $249.40  
  Purchase #4 $62.59   3.141%   $64.556   $64.56   $64.55   $64.60  
  Purchase #5 $156.70   12.104%   $175.667   $175.67   $175.65   $175.70  
  Purchase #6 $99.84   3.692%   $103.5261   $103.53   $103.55   $103.50  
  Purchase #7 $27.97   4.649%   $29.2703   $29.27   $29.25   $29.30  
  7 purchase totals = $875.13       $951.3008   $951.31   $951.25   $951.40