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	$174.39	7.759%	$187.9209	$187.92	$187.90	$187.90
Purchase #2	$168.70	6.545%	$179.7414	$179.74	$179.75	$179.70
Purchase #3	$105.96	11.103%	$117.7247	$117.72	$117.70	$117.70
Purchase #4	$40.80	8.452%	$44.2484	$44.25	$44.25	$44.20
Purchase #5	$39.26	10.482%	$43.3752	$43.38	$43.40	$43.40
Purchase #6	$76.54	3.109%	$78.9196	$78.92	$78.90	$78.90
Purchase #7	$227.28	9.333%	$248.492	$248.49	$248.50	$248.50
7 purchase totals =	$832.93		$900.4222	$900.42	$900.40	$900.30