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	$144.61	9.207%	$157.9242	$157.92	$157.90	$157.90
Purchase #2	$31.89	11.663%	$35.6093	$35.61	$35.60	$35.60
Purchase #3	$97.33	3.226%	$100.4699	$100.47	$100.45	$100.50
Purchase #4	$154.70	6.855%	$165.3047	$165.30	$165.30	$165.30
Purchase #5	$165.83	10.248%	$182.8243	$182.82	$182.80	$182.80
Purchase #6	$136.75	4.462%	$142.8518	$142.85	$142.85	$142.90
Purchase #7	$193.46	5.865%	$204.8064	$204.81	$204.80	$204.80
7 purchase totals =	$924.57		$989.7906	$989.78	$989.70	$989.80