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 $41.95   8.237%   $45.4054   $45.41   $45.40   $45.40  
  Purchase #2 $199.58   4.403%   $208.3675   $208.37   $208.35   $208.40  
  Purchase #3 $153.26   11.107%   $170.2826   $170.28   $170.30   $170.30  
  Purchase #4 $50.44   11.653%   $56.3178   $56.32   $56.30   $56.30  
  Purchase #5 $242.54   4.463%   $253.3646   $253.36   $253.35   $253.40  
  Purchase #6 $223.48   6.238%   $237.4207   $237.42   $237.40   $237.40  
  Purchase #7 $81.51   4.561%   $85.2277   $85.23   $85.25   $85.20  
  7 purchase totals = $992.76       $1,056.3863   $1,056.39   $1,056.35   $1,056.40