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 $203.84   11.830%   $227.9543   $227.95   $227.95   $228.00  
  Purchase #2 $57.26   8.566%   $62.1649   $62.16   $62.15   $62.20  
  Purchase #3 $59.51   9.726%   $65.2979   $65.30   $65.30   $65.30  
  Purchase #4 $122.74   10.468%   $135.5884   $135.59   $135.60   $135.60  
  Purchase #5 $72.85   11.580%   $81.286   $81.29   $81.30   $81.30  
  Purchase #6 $185.73   3.705%   $192.6113   $192.61   $192.60   $192.60  
  Purchase #7 $59.48   6.577%   $63.392   $63.39   $63.40   $63.40  
  7 purchase totals = $761.41       $828.2948   $828.29   $828.30   $828.40