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 $41.43   13.514%   $47.0289   $47.03   $47.05   $47.00  
  Purchase #2 $95.99   5.233%   $101.0132   $101.01   $101.00   $101.00  
  Purchase #3 $165.29   12.216%   $185.4818   $185.48   $185.50   $185.50  
  Purchase #4 $245.25   8.116%   $265.1545   $265.15   $265.15   $265.20  
  Purchase #5 $218.48   11.658%   $243.9504   $243.95   $243.95   $244.00  
  Purchase #6 $114.68   9.608%   $125.6985   $125.70   $125.70   $125.70  
  Purchase #7 $31.69   12.449%   $35.6351   $35.64   $35.65   $35.60  
  7 purchase totals = $912.81       $1,003.9624   $1,003.96   $1,004.00   $1,004.00