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 $63.27   10.577%   $69.9621   $69.96   $69.95   $70.00  
  Purchase #2 $19.29   7.666%   $20.7688   $20.77   $20.75   $20.80  
  Purchase #3 $148.91   12.162%   $167.0204   $167.02   $167.00   $167.00  
  Purchase #4 $208.28   4.850%   $218.3816   $218.38   $218.40   $218.40  
  Purchase #5 $249.77   3.244%   $257.8725   $257.87   $257.85   $257.90  
  Purchase #6 $231.69   13.312%   $262.5326   $262.53   $262.55   $262.50  
  Purchase #7 $12.64   12.703%   $14.2457   $14.25   $14.25   $14.20  
  7 purchase totals = $933.85       $1,010.7837   $1,010.78   $1,010.75   $1,010.80