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 $85.44   12.249%   $95.9055   $95.91   $95.90   $95.90  
  Purchase #2 $174.71   13.754%   $198.7396   $198.74   $198.75   $198.70  
  Purchase #3 $246.37   9.354%   $269.4154   $269.42   $269.40   $269.40  
  Purchase #4 $190.57   9.562%   $208.7923   $208.79   $208.80   $208.80  
  Purchase #5 $206.42   11.664%   $230.4968   $230.50   $230.50   $230.50  
  Purchase #6 $101.95   6.323%   $108.3963   $108.40   $108.40   $108.40  
  Purchase #7 $245.63   8.803%   $267.2528   $267.25   $267.25   $267.30  
  7 purchase totals = $1,251.09       $1,378.9987   $1,379.01   $1,379.00   $1,379.00