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 $124.31   8.193%   $134.4947   $134.49   $134.50   $134.50  
  Purchase #2 $208.26   11.545%   $232.3036   $232.30   $232.30   $232.30  
  Purchase #3 $77.86   7.402%   $83.6232   $83.62   $83.60   $83.60  
  Purchase #4 $55.98   10.294%   $61.7426   $61.74   $61.75   $61.70  
  Purchase #5 $115.51   8.442%   $125.2614   $125.26   $125.25   $125.30  
  Purchase #6 $132.54   12.184%   $148.6887   $148.69   $148.70   $148.70  
  Purchase #7 $16.68   13.471%   $18.927   $18.93   $18.95   $18.90  
  7 purchase totals = $731.14       $805.0412   $805.03   $805.05   $805.00