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	$21.36	7.253%	$22.9092	$22.91	$22.90	$22.90
Purchase #2	$73.49	3.559%	$76.1055	$76.11	$76.10	$76.10
Purchase #3	$71.31	7.747%	$76.8344	$76.83	$76.85	$76.80
Purchase #4	$180.56	7.298%	$193.7373	$193.74	$193.75	$193.70
Purchase #5	$90.66	9.519%	$99.2899	$99.29	$99.30	$99.30
Purchase #6	$229.42	11.248%	$255.2252	$255.23	$255.25	$255.20
Purchase #7	$101.33	10.115%	$111.5795	$111.58	$111.60	$111.60
7 purchase totals =	$768.13		$835.6810	$835.69	$835.75	$835.60