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 $221.84   13.607%   $252.0258   $252.03   $252.05   $252.00  
  Purchase #2 $161.62   12.343%   $181.5688   $181.57   $181.55   $181.60  
  Purchase #3 $42.38   13.348%   $48.0369   $48.04   $48.05   $48.00  
  Purchase #4 $222.86   8.113%   $240.9406   $240.94   $240.95   $240.90  
  Purchase #5 $219.68   12.128%   $246.3228   $246.32   $246.30   $246.30  
  Purchase #6 $102.66   3.733%   $106.4923   $106.49   $106.50   $106.50  
  Purchase #7 $69.33   5.509%   $73.1494   $73.15   $73.15   $73.10  
  7 purchase totals = $1,040.37       $1,148.5366   $1,148.54   $1,148.55   $1,148.40