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 $241.84   13.610%   $274.7544   $274.75   $274.75   $274.80  
  Purchase #2 $182.76   6.720%   $195.0415   $195.04   $195.05   $195.00  
  Purchase #3 $60.59   13.525%   $68.7848   $68.78   $68.80   $68.80  
  Purchase #4 $217.97   8.704%   $236.9421   $236.94   $236.95   $236.90  
  Purchase #5 $200.27   3.574%   $207.4276   $207.43   $207.45   $207.40  
  Purchase #6 $222.75   8.323%   $241.2895   $241.29   $241.30   $241.30  
  Purchase #7 $16.58   4.437%   $17.3157   $17.32   $17.30   $17.30  
  7 purchase totals = $1,142.76       $1,241.5556   $1,241.55   $1,241.60   $1,241.50