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 $248.61   7.477%   $267.1986   $267.20   $267.20   $267.20  
  Purchase #2 $72.99   12.165%   $81.8692   $81.87   $81.85   $81.90  
  Purchase #3 $173.73   4.568%   $181.666   $181.67   $181.65   $181.70  
  Purchase #4 $50.49   6.429%   $53.736   $53.74   $53.75   $53.70  
  Purchase #5 $211.28   9.828%   $232.0446   $232.04   $232.05   $232.00  
  Purchase #6 $177.78   4.549%   $185.8672   $185.87   $185.85   $185.90  
  Purchase #7 $57.42   8.845%   $62.4988   $62.50   $62.50   $62.50  
  7 purchase totals = $992.30       $1,064.8804   $1,064.89   $1,064.85   $1,064.90