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 $175.53   8.551%   $190.5396   $190.54   $190.55   $190.50  
  Purchase #2 $203.86   12.196%   $228.7228   $228.72   $228.70   $228.70  
  Purchase #3 $83.44   11.438%   $92.9839   $92.98   $93.00   $93.00  
  Purchase #4 $234.95   5.264%   $247.3178   $247.32   $247.30   $247.30  
  Purchase #5 $65.40   9.857%   $71.8465   $71.85   $71.85   $71.80  
  Purchase #6 $26.86   12.131%   $30.1184   $30.12   $30.10   $30.10  
  Purchase #7 $192.40   11.534%   $214.5914   $214.59   $214.60   $214.60  
  7 purchase totals = $982.44       $1,076.1204   $1,076.12   $1,076.10   $1,076.00