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 $58.68   8.157%   $63.4665   $63.47   $63.45   $63.50  
  Purchase #2 $46.30   5.550%   $48.8697   $48.87   $48.85   $48.90  
  Purchase #3 $207.33   7.181%   $222.2184   $222.22   $222.20   $222.20  
  Purchase #4 $140.47   5.367%   $148.009   $148.01   $148.00   $148.00  
  Purchase #5 $174.87   13.110%   $197.7955   $197.80   $197.80   $197.80  
  Purchase #6 $86.46   6.824%   $92.36   $92.36   $92.35   $92.40  
  Purchase #7 $240.84   12.728%   $271.4941   $271.49   $271.50   $271.50  
  7 purchase totals = $954.95       $1,044.2132   $1,044.22   $1,044.15   $1,044.30