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 $60.37   9.327%   $66.0007   $66.00   $66.00   $66.00  
  Purchase #2 $177.51   11.495%   $197.9148   $197.91   $197.90   $197.90  
  Purchase #3 $105.28   11.417%   $117.2998   $117.30   $117.30   $117.30  
  Purchase #4 $164.32   7.775%   $177.0959   $177.10   $177.10   $177.10  
  Purchase #5 $31.96   6.511%   $34.0409   $34.04   $34.05   $34.00  
  Purchase #6 $99.73   13.269%   $112.9632   $112.96   $112.95   $113.00  
  Purchase #7 $73.70   10.206%   $81.2218   $81.22   $81.20   $81.20  
  7 purchase totals = $712.87       $786.5371   $786.53   $786.50   $786.50