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 $91.82   4.430%   $95.8876   $95.89   $95.90   $95.90  
  Purchase #2 $210.32   12.653%   $236.9318   $236.93   $236.95   $236.90  
  Purchase #3 $91.69   7.769%   $98.8134   $98.81   $98.80   $98.80  
  Purchase #4 $12.67   10.277%   $13.9721   $13.97   $13.95   $14.00  
  Purchase #5 $120.77   7.301%   $129.5874   $129.59   $129.60   $129.60  
  Purchase #6 $21.28   7.669%   $22.912   $22.91   $22.90   $22.90  
  Purchase #7 $146.27   13.657%   $166.2461   $166.25   $166.25   $166.20  
  7 purchase totals = $694.82       $764.3504   $764.35   $764.35   $764.30