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 $116.95   6.750%   $124.8441   $124.84   $124.85   $124.80  
  Purchase #2 $203.67   13.457%   $231.0779   $231.08   $231.10   $231.10  
  Purchase #3 $11.30   8.158%   $12.2219   $12.22   $12.20   $12.20  
  Purchase #4 $58.36   10.156%   $64.287   $64.29   $64.30   $64.30  
  Purchase #5 $185.53   6.752%   $198.057   $198.06   $198.05   $198.10  
  Purchase #6 $197.54   5.554%   $208.5114   $208.51   $208.50   $208.50  
  Purchase #7 $162.96   9.541%   $178.508   $178.51   $178.50   $178.50  
  7 purchase totals = $936.31       $1,017.5073   $1,017.51   $1,017.50   $1,017.50