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 $190.42   12.372%   $213.9788   $213.98   $214.00   $214.00  
  Purchase #2 $209.33   6.822%   $223.6105   $223.61   $223.60   $223.60  
  Purchase #3 $247.88   10.195%   $273.1514   $273.15   $273.15   $273.20  
  Purchase #4 $44.41   4.277%   $46.3094   $46.31   $46.30   $46.30  
  Purchase #5 $85.38   12.175%   $95.775   $95.78   $95.80   $95.80  
  Purchase #6 $196.48   11.565%   $219.2029   $219.20   $219.20   $219.20  
  Purchase #7 $206.48   4.271%   $215.2988   $215.30   $215.30   $215.30  
  7 purchase totals = $1,180.38       $1,287.3268   $1,287.33   $1,287.35   $1,287.40