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	$100.62	13.171%	$113.8727	$113.87	$113.85	$113.90
Purchase #2	$240.61	12.339%	$270.2989	$270.30	$270.30	$270.30
Purchase #3	$82.47	7.479%	$88.6379	$88.64	$88.65	$88.60
Purchase #4	$250.78	9.658%	$275.0003	$275.00	$275.00	$275.00
Purchase #5	$53.84	10.545%	$59.5174	$59.52	$59.50	$59.50
Purchase #6	$184.73	7.839%	$199.211	$199.21	$199.20	$199.20
Purchase #7	$112.56	10.300%	$124.1537	$124.15	$124.15	$124.20
7 purchase totals =	$1,025.61		$1,130.6919	$1,130.69	$1,130.65	$1,130.70