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	$159.61	7.719%	$171.9303	$171.93	$171.95	$171.90
Purchase #2	$59.40	13.611%	$67.4849	$67.48	$67.50	$67.50
Purchase #3	$189.69	11.148%	$210.8366	$210.84	$210.85	$210.80
Purchase #4	$231.66	4.222%	$241.4407	$241.44	$241.45	$241.40
Purchase #5	$127.88	3.728%	$132.6474	$132.65	$132.65	$132.60
Purchase #6	$62.30	11.413%	$69.4103	$69.41	$69.40	$69.40
Purchase #7	$81.73	11.113%	$90.8127	$90.81	$90.80	$90.80
7 purchase totals =	$912.27		$984.5629	$984.56	$984.60	$984.40