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 $113.59   13.368%   $128.7747   $128.77   $128.75   $128.80  
  Purchase #2 $178.65   3.528%   $184.9528   $184.95   $184.95   $185.00  
  Purchase #3 $68.83   10.615%   $76.1363   $76.14   $76.15   $76.10  
  Purchase #4 $201.98   6.569%   $215.2481   $215.25   $215.25   $215.20  
  Purchase #5 $218.37   8.294%   $236.4816   $236.48   $236.50   $236.50  
  Purchase #6 $184.49   6.241%   $196.004   $196.00   $196.00   $196.00  
  Purchase #7 $149.87   13.237%   $169.7083   $169.71   $169.70   $169.70  
  7 purchase totals = $1,115.78       $1,207.3058   $1,207.30   $1,207.30   $1,207.30