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	$110.40	9.508%	$120.8968	$120.90	$120.90	$120.90
Purchase #2	$61.81	10.460%	$68.2753	$68.28	$68.30	$68.30
Purchase #3	$157.58	11.449%	$175.6213	$175.62	$175.60	$175.60
Purchase #4	$50.51	10.620%	$55.8742	$55.87	$55.85	$55.90
Purchase #5	$40.74	10.864%	$45.166	$45.17	$45.15	$45.20
Purchase #6	$56.52	5.705%	$59.7445	$59.74	$59.75	$59.70
Purchase #7	$131.57	9.188%	$143.6587	$143.66	$143.65	$143.70
7 purchase totals =	$609.13		$669.2368	$669.24	$669.20	$669.30