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 $88.79   11.193%   $98.7283   $98.73   $98.75   $98.70  
  Purchase #2 $59.57   10.813%   $66.0113   $66.01   $66.00   $66.00  
  Purchase #3 $173.67   6.744%   $185.3823   $185.38   $185.40   $185.40  
  Purchase #4 $208.78   6.651%   $222.666   $222.67   $222.65   $222.70  
  Purchase #5 $144.37   7.628%   $155.3825   $155.38   $155.40   $155.40  
  Purchase #6 $20.75   4.163%   $21.6138   $21.61   $21.60   $21.60  
  Purchase #7 $171.65   7.604%   $184.7023   $184.70   $184.70   $184.70  
  7 purchase totals = $867.58       $934.4865   $934.48   $934.50   $934.50