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 $202.85   13.614%   $230.466   $230.47   $230.45   $230.50  
  Purchase #2 $117.92   6.360%   $125.4197   $125.42   $125.40   $125.40  
  Purchase #3 $60.94   6.436%   $64.8621   $64.86   $64.85   $64.90  
  Purchase #4 $198.42   11.405%   $221.0498   $221.05   $221.05   $221.00  
  Purchase #5 $117.33   4.215%   $122.2755   $122.28   $122.30   $122.30  
  Purchase #6 $164.41   8.235%   $177.9492   $177.95   $177.95   $177.90  
  Purchase #7 $223.95   7.572%   $240.9075   $240.91   $240.90   $240.90  
  7 purchase totals = $1,085.82       $1,182.9298   $1,182.94   $1,182.90   $1,182.90