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 $233.62   5.398%   $246.2308   $246.23   $246.25   $246.20  
  Purchase #2 $97.90   11.345%   $109.0068   $109.01   $109.00   $109.00  
  Purchase #3 $125.68   8.389%   $136.2233   $136.22   $136.20   $136.20  
  Purchase #4 $108.83   8.738%   $118.3396   $118.34   $118.35   $118.30  
  Purchase #5 $162.47   10.838%   $180.0785   $180.08   $180.10   $180.10  
  Purchase #6 $164.51   10.121%   $181.1601   $181.16   $181.15   $181.20  
  Purchase #7 $73.48   3.690%   $76.1914   $76.19   $76.20   $76.20  
  7 purchase totals = $966.49       $1,047.2305   $1,047.23   $1,047.25   $1,047.20