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 $242.54   8.324%   $262.729   $262.73   $262.75   $262.70  
  Purchase #2 $99.74   10.319%   $110.0322   $110.03   $110.05   $110.00  
  Purchase #3 $13.31   5.250%   $14.0088   $14.01   $14.00   $14.00  
  Purchase #4 $55.47   10.527%   $61.3093   $61.31   $61.30   $61.30  
  Purchase #5 $194.62   4.183%   $202.761   $202.76   $202.75   $202.80  
  Purchase #6 $192.80   4.184%   $200.8668   $200.87   $200.85   $200.90  
  Purchase #7 $129.63   13.307%   $146.8799   $146.88   $146.90   $146.90  
  7 purchase totals = $928.11       $998.5870   $998.59   $998.60   $998.60