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 $93.76   11.603%   $104.639   $104.64   $104.65   $104.60  
  Purchase #2 $75.31   9.825%   $82.7092   $82.71   $82.70   $82.70  
  Purchase #3 $84.87   12.871%   $95.7936   $95.79   $95.80   $95.80  
  Purchase #4 $213.99   10.294%   $236.0181   $236.02   $236.00   $236.00  
  Purchase #5 $158.57   7.771%   $170.8925   $170.89   $170.90   $170.90  
  Purchase #6 $98.49   11.197%   $109.5179   $109.52   $109.50   $109.50  
  Purchase #7 $22.95   4.160%   $23.9047   $23.90   $23.90   $23.90  
  7 purchase totals = $747.94       $823.4750   $823.47   $823.45   $823.40