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 $240.92   11.327%   $268.209   $268.21   $268.20   $268.20  
  Purchase #2 $193.95   4.513%   $202.703   $202.70   $202.70   $202.70  
  Purchase #3 $60.96   11.737%   $68.1149   $68.11   $68.10   $68.10  
  Purchase #4 $174.80   7.352%   $187.6513   $187.65   $187.65   $187.70  
  Purchase #5 $70.71   3.662%   $73.2994   $73.30   $73.30   $73.30  
  Purchase #6 $99.74   12.314%   $112.022   $112.02   $112.00   $112.00  
  Purchase #7 $8.78   4.856%   $9.2064   $9.21   $9.20   $9.20  
  7 purchase totals = $849.86       $921.2060   $921.20   $921.15   $921.20