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 $145.41   4.669%   $152.1992   $152.20   $152.20   $152.20  
  Purchase #2 $149.93   9.308%   $163.8855   $163.89   $163.90   $163.90  
  Purchase #3 $189.92   12.470%   $213.603   $213.60   $213.60   $213.60  
  Purchase #4 $112.36   5.144%   $118.1398   $118.14   $118.15   $118.10  
  Purchase #5 $40.36   8.677%   $43.862   $43.86   $43.85   $43.90  
  Purchase #6 $236.42   12.614%   $266.242   $266.24   $266.25   $266.20  
  Purchase #7 $32.25   6.343%   $34.2956   $34.30   $34.30   $34.30  
  7 purchase totals = $906.65       $992.2271   $992.23   $992.25   $992.20