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 $35.58   6.311%   $37.8255   $37.83   $37.85   $37.80  
  Purchase #2 $193.88   4.566%   $202.7326   $202.73   $202.75   $202.70  
  Purchase #3 $216.60   11.259%   $240.987   $240.99   $241.00   $241.00  
  Purchase #4 $111.79   4.175%   $116.4572   $116.46   $116.45   $116.50  
  Purchase #5 $134.69   7.381%   $144.6315   $144.63   $144.65   $144.60  
  Purchase #6 $215.79   9.433%   $236.1455   $236.15   $236.15   $236.10  
  Purchase #7 $70.27   7.847%   $75.7841   $75.78   $75.80   $75.80  
  7 purchase totals = $978.60       $1,054.5634   $1,054.57   $1,054.65   $1,054.50