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	$236.39	13.404%	$268.0757	$268.08	$268.10	$268.10
Purchase #2	$7.89	13.173%	$8.9293	$8.93	$8.95	$8.90
Purchase #3	$81.46	9.731%	$89.3869	$89.39	$89.40	$89.40
Purchase #4	$208.51	5.421%	$219.8133	$219.81	$219.80	$219.80
Purchase #5	$230.91	11.327%	$257.0652	$257.07	$257.05	$257.10
Purchase #6	$129.51	13.137%	$146.5237	$146.52	$146.50	$146.50
Purchase #7	$138.57	9.360%	$151.5402	$151.54	$151.55	$151.50
7 purchase totals =	$1,033.24		$1,141.3343	$1,141.34	$1,141.35	$1,141.30