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 $71.55   3.137%   $73.7945   $73.79   $73.80   $73.80  
  Purchase #2 $172.30   13.588%   $195.7121   $195.71   $195.70   $195.70  
  Purchase #3 $69.26   13.192%   $78.3968   $78.40   $78.40   $78.40  
  Purchase #4 $230.36   12.830%   $259.9152   $259.92   $259.90   $259.90  
  Purchase #5 $165.86   3.540%   $171.7314   $171.73   $171.75   $171.70  
  Purchase #6 $165.50   7.678%   $178.2071   $178.21   $178.20   $178.20  
  Purchase #7 $62.49   6.652%   $66.6468   $66.65   $66.65   $66.60  
  7 purchase totals = $937.32       $1,024.4039   $1,024.41   $1,024.40   $1,024.30