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	$110.38	10.778%	$122.2768	$122.28	$122.30	$122.30
Purchase #2	$79.86	12.597%	$89.92	$89.92	$89.90	$89.90
Purchase #3	$180.26	5.713%	$190.5583	$190.56	$190.55	$190.60
Purchase #4	$164.91	4.482%	$172.3013	$172.30	$172.30	$172.30
Purchase #5	$102.55	12.434%	$115.3011	$115.30	$115.30	$115.30
Purchase #6	$34.31	10.257%	$37.8292	$37.83	$37.85	$37.80
Purchase #7	$59.42	8.261%	$64.3287	$64.33	$64.35	$64.30
7 purchase totals =	$731.69		$792.5154	$792.52	$792.55	$792.50