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	$54.61	9.527%	$59.8127	$59.81	$59.80	$59.80
Purchase #2	$194.66	4.463%	$203.3477	$203.35	$203.35	$203.30
Purchase #3	$174.30	11.476%	$194.3027	$194.30	$194.30	$194.30
Purchase #4	$39.73	5.785%	$42.0284	$42.03	$42.05	$42.00
Purchase #5	$224.30	8.350%	$243.0291	$243.03	$243.05	$243.00
Purchase #6	$56.52	7.191%	$60.5844	$60.58	$60.60	$60.60
Purchase #7	$51.42	10.139%	$56.6335	$56.63	$56.65	$56.60
7 purchase totals =	$795.54		$859.7385	$859.73	$859.80	$859.60