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 $172.52   13.467%   $195.7533   $195.75   $195.75   $195.80  
  Purchase #2 $198.72   11.599%   $221.7695   $221.77   $221.75   $221.80  
  Purchase #3 $107.61   7.793%   $115.996   $116.00   $116.00   $116.00  
  Purchase #4 $45.32   6.665%   $48.3406   $48.34   $48.35   $48.30  
  Purchase #5 $96.93   8.230%   $104.9073   $104.91   $104.90   $104.90  
  Purchase #6 $124.42   10.387%   $137.3435   $137.34   $137.35   $137.30  
  Purchase #7 $220.96   12.467%   $248.5071   $248.51   $248.50   $248.50  
  7 purchase totals = $966.48       $1,072.6173   $1,072.62   $1,072.60   $1,072.60