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 $88.63   6.302%   $94.2155   $94.22   $94.20   $94.20  
  Purchase #2 $121.42   4.366%   $126.7212   $126.72   $126.70   $126.70  
  Purchase #3 $140.73   13.694%   $160.0016   $160.00   $160.00   $160.00  
  Purchase #4 $127.85   7.170%   $137.0168   $137.02   $137.00   $137.00  
  Purchase #5 $90.84   7.184%   $97.3659   $97.37   $97.35   $97.40  
  Purchase #6 $119.77   8.117%   $129.4917   $129.49   $129.50   $129.50  
  Purchase #7 $27.65   10.517%   $30.558   $30.56   $30.55   $30.60  
  7 purchase totals = $716.89       $775.3707   $775.38   $775.30   $775.40