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	$128.98	12.473%	$145.0677	$145.07	$145.05	$145.10
Purchase #2	$18.83	7.780%	$20.295	$20.30	$20.30	$20.30
Purchase #3	$34.50	9.860%	$37.9017	$37.90	$37.90	$37.90
Purchase #4	$32.61	3.139%	$33.6336	$33.63	$33.65	$33.60
Purchase #5	$84.47	5.502%	$89.1175	$89.12	$89.10	$89.10
Purchase #6	$198.52	4.306%	$207.0683	$207.07	$207.05	$207.10
Purchase #7	$228.25	12.195%	$256.0851	$256.09	$256.10	$256.10
7 purchase totals =	$726.16		$789.1689	$789.18	$789.15	$789.20