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 $222.75   8.190%   $240.9932   $240.99   $241.00   $241.00  
  Purchase #2 $143.65   6.688%   $153.2573   $153.26   $153.25   $153.30  
  Purchase #3 $206.43   6.868%   $220.6076   $220.61   $220.60   $220.60  
  Purchase #4 $169.96   3.285%   $175.5432   $175.54   $175.55   $175.50  
  Purchase #5 $100.48   13.803%   $114.3493   $114.35   $114.35   $114.30  
  Purchase #6 $243.42   9.518%   $266.5887   $266.59   $266.60   $266.60  
  Purchase #7 $182.57   4.340%   $190.4935   $190.49   $190.50   $190.50  
  7 purchase totals = $1,269.26       $1,361.8328   $1,361.83   $1,361.85   $1,361.80