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 $181.68   13.579%   $206.3503   $206.35   $206.35   $206.40  
  Purchase #2 $249.52   10.607%   $275.9866   $275.99   $276.00   $276.00  
  Purchase #3 $96.94   3.649%   $100.4773   $100.48   $100.50   $100.50  
  Purchase #4 $248.40   10.692%   $274.9589   $274.96   $274.95   $275.00  
  Purchase #5 $172.47   6.730%   $184.0772   $184.08   $184.10   $184.10  
  Purchase #6 $239.44   8.726%   $260.3335   $260.33   $260.35   $260.30  
  Purchase #7 $69.28   8.296%   $75.0275   $75.03   $75.05   $75.00  
  7 purchase totals = $1,257.73       $1,377.2113   $1,377.22   $1,377.30   $1,377.30