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 $240.44   4.119%   $250.3437   $250.34   $250.35   $250.30  
  Purchase #2 $113.49   13.148%   $128.4117   $128.41   $128.40   $128.40  
  Purchase #3 $29.40   12.139%   $32.9689   $32.97   $32.95   $33.00  
  Purchase #4 $205.42   6.575%   $218.9264   $218.93   $218.95   $218.90  
  Purchase #5 $193.94   13.580%   $220.2771   $220.28   $220.30   $220.30  
  Purchase #6 $233.46   13.159%   $264.181   $264.18   $264.20   $264.20  
  Purchase #7 $49.58   8.574%   $53.831   $53.83   $53.85   $53.80  
  7 purchase totals = $1,065.73       $1,168.9398   $1,168.94   $1,169.00   $1,168.90