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	$92.28	8.846%	$100.4431	$100.44	$100.45	$100.40
Purchase #2	$27.59	11.492%	$30.7606	$30.76	$30.75	$30.80
Purchase #3	$79.40	13.150%	$89.8411	$89.84	$89.85	$89.80
Purchase #4	$169.69	7.254%	$181.9993	$182.00	$182.00	$182.00
Purchase #5	$9.72	8.105%	$10.5078	$10.51	$10.50	$10.50
Purchase #6	$73.83	11.546%	$82.3544	$82.35	$82.35	$82.40
Purchase #7	$90.82	3.203%	$93.729	$93.73	$93.75	$93.70
7 purchase totals =	$543.33		$589.6353	$589.63	$589.65	$589.60