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 $227.58   11.177%   $253.0166   $253.02   $253.00   $253.00  
  Purchase #2 $218.86   11.818%   $244.7249   $244.72   $244.70   $244.70  
  Purchase #3 $190.56   6.396%   $202.7482   $202.75   $202.75   $202.70  
  Purchase #4 $160.30   8.179%   $173.4109   $173.41   $173.40   $173.40  
  Purchase #5 $31.72   13.244%   $35.921   $35.92   $35.90   $35.90  
  Purchase #6 $130.37   9.277%   $142.4644   $142.46   $142.45   $142.50  
  Purchase #7 $70.36   11.305%   $78.3142   $78.31   $78.30   $78.30  
  7 purchase totals = $1,029.75       $1,130.6002   $1,130.59   $1,130.50   $1,130.50