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 $244.73   6.554%   $260.7696   $260.77   $260.75   $260.80  
  Purchase #2 $116.26   11.697%   $129.8589   $129.86   $129.85   $129.90  
  Purchase #3 $225.62   9.830%   $247.7984   $247.80   $247.80   $247.80  
  Purchase #4 $219.46   3.628%   $227.422   $227.42   $227.40   $227.40  
  Purchase #5 $151.66   9.679%   $166.3392   $166.34   $166.35   $166.30  
  Purchase #6 $178.46   13.334%   $202.2559   $202.26   $202.25   $202.30  
  Purchase #7 $241.85   3.764%   $250.9532   $250.95   $250.95   $251.00  
  7 purchase totals = $1,378.04       $1,485.3972   $1,485.40   $1,485.35   $1,485.50