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 $53.71   6.644%   $57.2785   $57.28   $57.30   $57.30  
  Purchase #2 $213.27   13.788%   $242.6757   $242.68   $242.70   $242.70  
  Purchase #3 $244.47   13.841%   $278.3071   $278.31   $278.30   $278.30  
  Purchase #4 $94.92   9.164%   $103.6185   $103.62   $103.60   $103.60  
  Purchase #5 $247.80   8.149%   $267.9932   $267.99   $268.00   $268.00  
  Purchase #6 $153.75   9.770%   $168.7714   $168.77   $168.75   $168.80  
  Purchase #7 $36.53   5.607%   $38.5782   $38.58   $38.60   $38.60  
  7 purchase totals = $1,044.45       $1,157.2226   $1,157.23   $1,157.25   $1,157.30