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 $52.70   13.794%   $59.9694   $59.97   $59.95   $60.00  
  Purchase #2 $148.73   11.448%   $165.7566   $165.76   $165.75   $165.80  
  Purchase #3 $112.98   5.308%   $118.977   $118.98   $119.00   $119.00  
  Purchase #4 $8.93   3.560%   $9.2479   $9.25   $9.25   $9.20  
  Purchase #5 $243.44   5.529%   $256.8998   $256.90   $256.90   $256.90  
  Purchase #6 $47.49   10.771%   $52.6051   $52.61   $52.60   $52.60  
  Purchase #7 $179.44   6.705%   $191.4715   $191.47   $191.45   $191.50  
  7 purchase totals = $793.71       $854.9273   $854.94   $854.90   $855.00