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 $203.77   5.513%   $215.0038   $215.00   $215.00   $215.00  
  Purchase #2 $149.57   3.403%   $154.6599   $154.66   $154.65   $154.70  
  Purchase #3 $166.33   4.250%   $173.399   $173.40   $173.40   $173.40  
  Purchase #4 $89.32   9.418%   $97.7322   $97.73   $97.75   $97.70  
  Purchase #5 $5.91   11.636%   $6.5977   $6.60   $6.60   $6.60  
  Purchase #6 $91.53   11.786%   $102.3177   $102.32   $102.30   $102.30  
  Purchase #7 $216.96   3.206%   $223.9157   $223.92   $223.90   $223.90  
  7 purchase totals = $923.39       $973.6260   $973.63   $973.60   $973.60