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 $228.42   6.434%   $243.1165   $243.12   $243.10   $243.10  
  Purchase #2 $164.28   10.136%   $180.9314   $180.93   $180.95   $180.90  
  Purchase #3 $94.95   12.583%   $106.8976   $106.90   $106.90   $106.90  
  Purchase #4 $246.99   11.154%   $274.5393   $274.54   $274.55   $274.50  
  Purchase #5 $41.35   12.255%   $46.4174   $46.42   $46.40   $46.40  
  Purchase #6 $139.85   4.659%   $146.3656   $146.37   $146.35   $146.40  
  Purchase #7 $169.86   6.182%   $180.3607   $180.36   $180.35   $180.40  
  7 purchase totals = $1,085.70       $1,178.6285   $1,178.64   $1,178.60   $1,178.60