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	$39.89	7.692%	$42.9583	$42.96	$42.95	$43.00
Purchase #2	$86.41	3.477%	$89.4145	$89.41	$89.40	$89.40
Purchase #3	$99.55	5.766%	$105.2901	$105.29	$105.30	$105.30
Purchase #4	$174.53	6.658%	$186.1502	$186.15	$186.15	$186.20
Purchase #5	$140.32	10.103%	$154.4965	$154.50	$154.50	$154.50
Purchase #6	$204.80	8.238%	$221.6714	$221.67	$221.65	$221.70
Purchase #7	$74.43	3.120%	$76.7522	$76.75	$76.75	$76.80
7 purchase totals =	$819.93		$876.7332	$876.73	$876.70	$876.90