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 $219.29   12.553%   $246.8175   $246.82   $246.80   $246.80  
  Purchase #2 $170.93   4.491%   $178.6065   $178.61   $178.60   $178.60  
  Purchase #3 $127.34   9.137%   $138.9751   $138.98   $139.00   $139.00  
  Purchase #4 $189.39   6.409%   $201.528   $201.53   $201.55   $201.50  
  Purchase #5 $22.32   12.584%   $25.1287   $25.13   $25.15   $25.10  
  Purchase #6 $132.90   5.784%   $140.5869   $140.59   $140.60   $140.60  
  Purchase #7 $154.50   6.206%   $164.0883   $164.09   $164.10   $164.10  
  7 purchase totals = $1,016.67       $1,095.7310   $1,095.75   $1,095.80   $1,095.70