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 $240.97   8.252%   $260.8548   $260.85   $260.85   $260.90  
  Purchase #2 $232.66   6.491%   $247.762   $247.76   $247.75   $247.80  
  Purchase #3 $77.79   5.288%   $81.9035   $81.90   $81.90   $81.90  
  Purchase #4 $248.37   7.333%   $266.583   $266.58   $266.60   $266.60  
  Purchase #5 $48.53   5.838%   $51.3632   $51.36   $51.35   $51.40  
  Purchase #6 $13.80   8.534%   $14.9777   $14.98   $15.00   $15.00  
  Purchase #7 $94.99   6.169%   $100.8499   $100.85   $100.85   $100.80  
  7 purchase totals = $957.11       $1,024.2941   $1,024.28   $1,024.30   $1,024.40