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	$64.63	12.794%	$72.8988	$72.90	$72.90	$72.90
Purchase #2	$26.78	3.731%	$27.7792	$27.78	$27.80	$27.80
Purchase #3	$126.74	13.494%	$143.8423	$143.84	$143.85	$143.80
Purchase #4	$137.28	11.303%	$152.7968	$152.80	$152.80	$152.80
Purchase #5	$197.41	6.808%	$210.8497	$210.85	$210.85	$210.80
Purchase #6	$38.79	12.751%	$43.7361	$43.74	$43.75	$43.70
Purchase #7	$50.85	5.463%	$53.6279	$53.63	$53.65	$53.60
7 purchase totals =	$642.48		$705.5308	$705.54	$705.60	$705.40