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 $233.46   10.732%   $258.5149   $258.51   $258.50   $258.50  
  Purchase #2 $148.50   4.140%   $154.6479   $154.65   $154.65   $154.60  
  Purchase #3 $49.89   9.581%   $54.67   $54.67   $54.65   $54.70  
  Purchase #4 $239.42   9.648%   $262.5192   $262.52   $262.50   $262.50  
  Purchase #5 $242.53   9.762%   $266.2058   $266.21   $266.20   $266.20  
  Purchase #6 $146.68   9.743%   $160.971   $160.97   $160.95   $161.00  
  Purchase #7 $210.55   4.230%   $219.4563   $219.46   $219.45   $219.50  
  7 purchase totals = $1,271.03       $1,376.9851   $1,376.99   $1,376.90   $1,377.00