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 $181.99   11.566%   $203.039   $203.04   $203.05   $203.00  
  Purchase #2 $121.86   3.388%   $125.9886   $125.99   $126.00   $126.00  
  Purchase #3 $96.86   11.462%   $107.9621   $107.96   $107.95   $108.00  
  Purchase #4 $224.69   5.272%   $236.5357   $236.54   $236.55   $236.50  
  Purchase #5 $234.74   13.416%   $266.2327   $266.23   $266.25   $266.20  
  Purchase #6 $236.74   13.569%   $268.8633   $268.86   $268.85   $268.90  
  Purchase #7 $68.37   13.839%   $77.8317   $77.83   $77.85   $77.80  
  7 purchase totals = $1,165.25       $1,286.4531   $1,286.45   $1,286.50   $1,286.40