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 $95.86   6.678%   $102.2615   $102.26   $102.25   $102.30  
  Purchase #2 $213.83   10.625%   $236.5494   $236.55   $236.55   $236.50  
  Purchase #3 $91.85   7.642%   $98.8692   $98.87   $98.85   $98.90  
  Purchase #4 $219.67   6.737%   $234.4692   $234.47   $234.45   $234.50  
  Purchase #5 $222.71   11.126%   $247.4887   $247.49   $247.50   $247.50  
  Purchase #6 $172.46   11.209%   $191.791   $191.79   $191.80   $191.80  
  Purchase #7 $20.69   12.443%   $23.2645   $23.26   $23.25   $23.30  
  7 purchase totals = $1,037.07       $1,134.6935   $1,134.69   $1,134.65   $1,134.80