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	$20.37	10.220%	$22.4518	$22.45	$22.45	$22.50
Purchase #2	$101.72	10.389%	$112.2877	$112.29	$112.30	$112.30
Purchase #3	$79.44	13.818%	$90.417	$90.42	$90.40	$90.40
Purchase #4	$146.33	3.708%	$151.7559	$151.76	$151.75	$151.80
Purchase #5	$81.36	13.733%	$92.5332	$92.53	$92.55	$92.50
Purchase #6	$224.25	13.200%	$253.851	$253.85	$253.85	$253.90
Purchase #7	$236.75	9.391%	$258.9832	$258.98	$259.00	$259.00
7 purchase totals =	$890.22		$982.2798	$982.28	$982.30	$982.40