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 $73.53   3.627%   $76.1969   $76.20   $76.20   $76.20  
  Purchase #2 $8.49   8.176%   $9.1841   $9.18   $9.20   $9.20  
  Purchase #3 $151.41   12.128%   $169.773   $169.77   $169.75   $169.80  
  Purchase #4 $20.37   11.162%   $22.6437   $22.64   $22.65   $22.60  
  Purchase #5 $91.35   3.582%   $94.6222   $94.62   $94.60   $94.60  
  Purchase #6 $227.49   3.829%   $236.2006   $236.20   $236.20   $236.20  
  Purchase #7 $232.31   5.834%   $245.863   $245.86   $245.85   $245.90  
  7 purchase totals = $804.95       $854.4835   $854.47   $854.45   $854.50