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 $104.98   6.694%   $112.0074   $112.01   $112.00   $112.00  
  Purchase #2 $211.29   6.444%   $224.9055   $224.91   $224.90   $224.90  
  Purchase #3 $176.83   6.553%   $188.4177   $188.42   $188.40   $188.40  
  Purchase #4 $155.93   6.594%   $166.212   $166.21   $166.20   $166.20  
  Purchase #5 $232.48   5.417%   $245.0734   $245.07   $245.05   $245.10  
  Purchase #6 $211.36   10.840%   $234.2714   $234.27   $234.25   $234.30  
  Purchase #7 $73.60   8.625%   $79.948   $79.95   $79.95   $79.90  
  7 purchase totals = $1,166.47       $1,250.8354   $1,250.84   $1,250.75   $1,250.80