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 $142.42   7.590%   $153.2297   $153.23   $153.25   $153.20  
  Purchase #2 $168.63   13.179%   $190.8537   $190.85   $190.85   $190.90  
  Purchase #3 $125.45   12.151%   $140.6934   $140.69   $140.70   $140.70  
  Purchase #4 $232.30   6.329%   $247.0023   $247.00   $247.00   $247.00  
  Purchase #5 $192.43   9.384%   $210.4876   $210.49   $210.50   $210.50  
  Purchase #6 $238.92   12.596%   $269.0144   $269.01   $269.00   $269.00  
  Purchase #7 $103.48   11.573%   $115.4557   $115.46   $115.45   $115.50  
  7 purchase totals = $1,203.63       $1,326.7368   $1,326.73   $1,326.75   $1,326.80