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 $95.63   3.507%   $98.9837   $98.98   $99.00   $99.00  
  Purchase #2 $215.41   6.221%   $228.8107   $228.81   $228.80   $228.80  
  Purchase #3 $204.80   5.784%   $216.6456   $216.65   $216.65   $216.60  
  Purchase #4 $216.42   11.803%   $241.9641   $241.96   $241.95   $242.00  
  Purchase #5 $29.57   3.182%   $30.5109   $30.51   $30.50   $30.50  
  Purchase #6 $88.49   11.355%   $98.538   $98.54   $98.55   $98.50  
  Purchase #7 $210.47   12.368%   $236.5009   $236.50   $236.50   $236.50  
  7 purchase totals = $1,060.79       $1,151.9539   $1,151.95   $1,151.95   $1,151.90