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 $24.63   6.579%   $26.2504   $26.25   $26.25   $26.30  
  Purchase #2 $98.91   8.853%   $107.6665   $107.67   $107.65   $107.70  
  Purchase #3 $173.89   11.574%   $194.016   $194.02   $194.00   $194.00  
  Purchase #4 $65.73   4.352%   $68.5906   $68.59   $68.60   $68.60  
  Purchase #5 $37.52   10.374%   $41.4123   $41.41   $41.40   $41.40  
  Purchase #6 $237.56   12.391%   $266.9961   $267.00   $267.00   $267.00  
  Purchase #7 $154.27   3.236%   $159.2622   $159.26   $159.25   $159.30  
  7 purchase totals = $792.51       $864.1941   $864.20   $864.15   $864.30