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 $71.49   6.734%   $76.3041   $76.30   $76.30   $76.30  
  Purchase #2 $198.27   7.859%   $213.852   $213.85   $213.85   $213.90  
  Purchase #3 $121.38   8.444%   $131.6293   $131.63   $131.65   $131.60  
  Purchase #4 $209.92   7.447%   $225.5527   $225.55   $225.55   $225.60  
  Purchase #5 $15.26   9.123%   $16.6522   $16.65   $16.65   $16.70  
  Purchase #6 $194.61   7.647%   $209.4918   $209.49   $209.50   $209.50  
  Purchase #7 $125.41   3.656%   $129.995   $130.00   $130.00   $130.00  
  7 purchase totals = $936.34       $1,003.4771   $1,003.47   $1,003.50   $1,003.60