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 $62.91   5.256%   $66.2165   $66.22   $66.20   $66.20  
  Purchase #2 $153.66   10.260%   $169.4255   $169.43   $169.45   $169.40  
  Purchase #3 $151.39   10.613%   $167.457   $167.46   $167.45   $167.50  
  Purchase #4 $191.37   13.490%   $217.1858   $217.19   $217.20   $217.20  
  Purchase #5 $21.59   8.257%   $23.3727   $23.37   $23.35   $23.40  
  Purchase #6 $38.60   12.665%   $43.4887   $43.49   $43.50   $43.50  
  Purchase #7 $79.98   7.609%   $86.0657   $86.07   $86.05   $86.10  
  7 purchase totals = $699.50       $773.2119   $773.23   $773.20   $773.30