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 $53.93   5.253%   $56.7629   $56.76   $56.75   $56.80  
  Purchase #2 $111.50   11.306%   $124.1062   $124.11   $124.10   $124.10  
  Purchase #3 $223.48   9.654%   $245.0548   $245.05   $245.05   $245.10  
  Purchase #4 $250.43   8.391%   $271.4436   $271.44   $271.45   $271.40  
  Purchase #5 $185.55   11.419%   $206.738   $206.74   $206.75   $206.70  
  Purchase #6 $89.70   3.230%   $92.5973   $92.60   $92.60   $92.60  
  Purchase #7 $110.32   6.589%   $117.589   $117.59   $117.60   $117.60  
  7 purchase totals = $1,024.91       $1,114.2918   $1,114.29   $1,114.30   $1,114.30