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 $97.46   13.636%   $110.7496   $110.75   $110.75   $110.70  
  Purchase #2 $224.77   5.458%   $237.0379   $237.04   $237.05   $237.00  
  Purchase #3 $24.48   5.185%   $25.7493   $25.75   $25.75   $25.70  
  Purchase #4 $88.52   11.471%   $98.6741   $98.67   $98.65   $98.70  
  Purchase #5 $92.72   7.478%   $99.6536   $99.65   $99.65   $99.70  
  Purchase #6 $250.43   12.585%   $281.9466   $281.95   $281.95   $281.90  
  Purchase #7 $59.49   8.477%   $64.533   $64.53   $64.55   $64.50  
  7 purchase totals = $837.87       $918.3441   $918.34   $918.35   $918.20