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 $94.37   4.497%   $98.6138   $98.61   $98.60   $98.60  
  Purchase #2 $209.76   12.609%   $236.2086   $236.21   $236.20   $236.20  
  Purchase #3 $123.41   9.162%   $134.7168   $134.72   $134.70   $134.70  
  Purchase #4 $121.55   5.162%   $127.8244   $127.82   $127.80   $127.80  
  Purchase #5 $241.78   3.410%   $250.0247   $250.02   $250.00   $250.00  
  Purchase #6 $153.34   12.403%   $172.3588   $172.36   $172.35   $172.40  
  Purchase #7 $214.86   8.233%   $232.5494   $232.55   $232.55   $232.50  
  7 purchase totals = $1,159.07       $1,252.2965   $1,252.29   $1,252.20   $1,252.20