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 $192.50   12.703%   $216.9533   $216.95   $216.95   $217.00  
  Purchase #2 $172.46   7.448%   $185.3048   $185.30   $185.30   $185.30  
  Purchase #3 $195.91   5.418%   $206.5244   $206.52   $206.50   $206.50  
  Purchase #4 $68.41   11.644%   $76.3757   $76.38   $76.40   $76.40  
  Purchase #5 $54.80   10.297%   $60.4428   $60.44   $60.45   $60.40  
  Purchase #6 $141.33   8.681%   $153.5989   $153.60   $153.60   $153.60  
  Purchase #7 $177.65   8.235%   $192.2795   $192.28   $192.30   $192.30  
  7 purchase totals = $1,003.06       $1,091.4794   $1,091.47   $1,091.50   $1,091.50