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 $59.98   10.856%   $66.4914   $66.49   $66.50   $66.50  
  Purchase #2 $96.98   9.339%   $106.037   $106.04   $106.05   $106.00  
  Purchase #3 $125.97   9.158%   $137.5063   $137.51   $137.50   $137.50  
  Purchase #4 $45.73   9.247%   $49.9587   $49.96   $49.95   $50.00  
  Purchase #5 $174.40   6.312%   $185.4081   $185.41   $185.40   $185.40  
  Purchase #6 $208.43   13.739%   $237.0662   $237.07   $237.05   $237.10  
  Purchase #7 $86.85   6.773%   $92.7324   $92.73   $92.75   $92.70  
  7 purchase totals = $798.34       $875.2001   $875.21   $875.20   $875.20