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	$158.86	13.307%	$179.9995	$180.00	$180.00	$180.00
Purchase #2	$54.29	13.312%	$61.5171	$61.52	$61.50	$61.50
Purchase #3	$188.43	10.251%	$207.746	$207.75	$207.75	$207.70
Purchase #4	$10.61	3.290%	$10.9591	$10.96	$10.95	$11.00
Purchase #5	$64.67	4.872%	$67.8207	$67.82	$67.80	$67.80
Purchase #6	$65.65	11.143%	$72.9654	$72.97	$72.95	$73.00
Purchase #7	$97.96	7.737%	$105.5392	$105.54	$105.55	$105.50
7 purchase totals =	$640.47		$706.5470	$706.56	$706.50	$706.50