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 $145.86   9.578%   $159.8305   $159.83   $159.85   $159.80  
  Purchase #2 $234.50   4.766%   $245.6763   $245.68   $245.70   $245.70  
  Purchase #3 $137.47   3.783%   $142.6705   $142.67   $142.65   $142.70  
  Purchase #4 $69.84   9.527%   $76.4937   $76.49   $76.50   $76.50  
  Purchase #5 $47.34   5.322%   $49.8594   $49.86   $49.85   $49.90  
  Purchase #6 $180.59   6.393%   $192.1351   $192.14   $192.15   $192.10  
  Purchase #7 $199.62   5.832%   $211.2618   $211.26   $211.25   $211.30  
  7 purchase totals = $1,015.22       $1,077.9273   $1,077.93   $1,077.95   $1,078.00