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 $58.92   7.740%   $63.4804   $63.48   $63.50   $63.50  
  Purchase #2 $150.28   5.267%   $158.1952   $158.20   $158.20   $158.20  
  Purchase #3 $69.44   7.252%   $74.4758   $74.48   $74.50   $74.50  
  Purchase #4 $220.44   11.171%   $245.0654   $245.07   $245.05   $245.10  
  Purchase #5 $250.93   3.166%   $258.8744   $258.87   $258.85   $258.90  
  Purchase #6 $144.58   3.681%   $149.902   $149.90   $149.90   $149.90  
  Purchase #7 $71.44   4.345%   $74.5441   $74.54   $74.55   $74.50  
  7 purchase totals = $966.03       $1,024.5373   $1,024.54   $1,024.55   $1,024.60