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 $208.53   13.159%   $235.9705   $235.97   $235.95   $236.00  
  Purchase #2 $92.81   11.752%   $103.717   $103.72   $103.70   $103.70  
  Purchase #3 $102.33   4.781%   $107.2224   $107.22   $107.20   $107.20  
  Purchase #4 $35.32   12.847%   $39.8576   $39.86   $39.85   $39.90  
  Purchase #5 $193.80   8.751%   $210.7594   $210.76   $210.75   $210.80  
  Purchase #6 $121.63   7.317%   $130.5297   $130.53   $130.55   $130.50  
  Purchase #7 $245.26   13.815%   $279.1427   $279.14   $279.15   $279.10  
  7 purchase totals = $999.68       $1,107.1993   $1,107.20   $1,107.15   $1,107.20