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 $208.98   12.218%   $234.5132   $234.51   $234.50   $234.50  
  Purchase #2 $154.97   5.343%   $163.25   $163.25   $163.25   $163.30  
  Purchase #3 $91.38   12.781%   $103.0593   $103.06   $103.05   $103.10  
  Purchase #4 $122.35   10.663%   $135.3962   $135.40   $135.40   $135.40  
  Purchase #5 $205.97   4.804%   $215.8648   $215.86   $215.85   $215.90  
  Purchase #6 $192.69   12.685%   $217.1327   $217.13   $217.15   $217.10  
  Purchase #7 $157.27   3.580%   $162.9003   $162.90   $162.90   $162.90  
  7 purchase totals = $1,133.61       $1,232.1165   $1,232.11   $1,232.10   $1,232.20