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 $68.36   3.283%   $70.6043   $70.60   $70.60   $70.60  
  Purchase #2 $76.49   3.545%   $79.2016   $79.20   $79.20   $79.20  
  Purchase #3 $250.42   13.485%   $284.1891   $284.19   $284.20   $284.20  
  Purchase #4 $98.66   13.511%   $111.99   $111.99   $112.00   $112.00  
  Purchase #5 $229.42   11.430%   $255.6427   $255.64   $255.65   $255.60  
  Purchase #6 $77.25   8.449%   $83.7769   $83.78   $83.80   $83.80  
  Purchase #7 $162.51   3.621%   $168.3945   $168.39   $168.40   $168.40  
  7 purchase totals = $963.11       $1,053.7991   $1,053.79   $1,053.85   $1,053.80