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 $191.93   6.165%   $203.7625   $203.76   $203.75   $203.80  
  Purchase #2 $50.41   5.209%   $53.0359   $53.04   $53.05   $53.00  
  Purchase #3 $43.59   7.298%   $46.7712   $46.77   $46.75   $46.80  
  Purchase #4 $190.76   9.130%   $208.1764   $208.18   $208.20   $208.20  
  Purchase #5 $204.53   10.136%   $225.2612   $225.26   $225.25   $225.30  
  Purchase #6 $69.98   9.276%   $76.4713   $76.47   $76.45   $76.50  
  Purchase #7 $185.51   8.297%   $200.9018   $200.90   $200.90   $200.90  
  7 purchase totals = $936.71       $1,014.3803   $1,014.38   $1,014.35   $1,014.50