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 $246.51   5.608%   $260.3343   $260.33   $260.35   $260.30  
  Purchase #2 $76.84   13.540%   $87.2441   $87.24   $87.25   $87.20  
  Purchase #3 $139.84   3.227%   $144.3526   $144.35   $144.35   $144.40  
  Purchase #4 $197.45   3.605%   $204.5681   $204.57   $204.55   $204.60  
  Purchase #5 $169.66   12.276%   $190.4875   $190.49   $190.50   $190.50  
  Purchase #6 $244.53   8.809%   $266.0706   $266.07   $266.05   $266.10  
  Purchase #7 $230.83   4.482%   $241.1758   $241.18   $241.20   $241.20  
  7 purchase totals = $1,305.66       $1,394.2330   $1,394.23   $1,394.25   $1,394.30