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 $90.86   4.464%   $94.916   $94.92   $94.90   $94.90  
  Purchase #2 $60.56   5.170%   $63.691   $63.69   $63.70   $63.70  
  Purchase #3 $136.30   13.564%   $154.7877   $154.79   $154.80   $154.80  
  Purchase #4 $215.42   5.450%   $227.1604   $227.16   $227.15   $227.20  
  Purchase #5 $13.75   3.456%   $14.2252   $14.23   $14.25   $14.20  
  Purchase #6 $105.79   3.795%   $109.8047   $109.80   $109.80   $109.80  
  Purchase #7 $180.38   5.280%   $189.9041   $189.90   $189.90   $189.90  
  7 purchase totals = $803.06       $854.4891   $854.49   $854.50   $854.50