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	$109.73	6.108%	$116.4323	$116.43	$116.45	$116.40
Purchase #2	$120.41	7.562%	$129.5154	$129.52	$129.50	$129.50
Purchase #3	$215.52	13.256%	$244.0893	$244.09	$244.10	$244.10
Purchase #4	$250.61	5.140%	$263.4914	$263.49	$263.50	$263.50
Purchase #5	$23.63	6.700%	$25.2132	$25.21	$25.20	$25.20
Purchase #6	$49.28	10.255%	$54.3337	$54.33	$54.35	$54.30
Purchase #7	$53.98	9.580%	$59.1513	$59.15	$59.15	$59.20
7 purchase totals =	$823.16		$892.2266	$892.22	$892.25	$892.20