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 $233.57   5.842%   $247.2152   $247.22   $247.20   $247.20  
  Purchase #2 $8.30   9.839%   $9.1166   $9.12   $9.10   $9.10  
  Purchase #3 $174.43   12.138%   $195.6023   $195.60   $195.60   $195.60  
  Purchase #4 $90.92   12.769%   $102.5296   $102.53   $102.55   $102.50  
  Purchase #5 $10.56   9.241%   $11.5358   $11.54   $11.55   $11.50  
  Purchase #6 $199.70   3.271%   $206.2322   $206.23   $206.25   $206.20  
  Purchase #7 $234.42   7.608%   $252.2547   $252.25   $252.25   $252.30  
  7 purchase totals = $951.90       $1,024.4864   $1,024.49   $1,024.50   $1,024.40