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 $117.50   5.708%   $124.2069   $124.21   $124.20   $124.20  
  Purchase #2 $76.41   3.206%   $78.8597   $78.86   $78.85   $78.90  
  Purchase #3 $157.29   6.808%   $167.9983   $168.00   $168.00   $168.00  
  Purchase #4 $214.56   11.792%   $239.8609   $239.86   $239.85   $239.90  
  Purchase #5 $34.59   12.304%   $38.846   $38.85   $38.85   $38.80  
  Purchase #6 $232.72   8.723%   $253.0202   $253.02   $253.00   $253.00  
  Purchase #7 $247.88   13.749%   $281.961   $281.96   $281.95   $282.00  
  7 purchase totals = $1,080.95       $1,184.7530   $1,184.76   $1,184.70   $1,184.80