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	$69.50	12.247%	$78.0117	$78.01	$78.00	$78.00
Purchase #2	$153.42	6.130%	$162.8246	$162.82	$162.80	$162.80
Purchase #3	$86.53	5.639%	$91.4094	$91.41	$91.40	$91.40
Purchase #4	$51.69	8.652%	$56.1622	$56.16	$56.15	$56.20
Purchase #5	$54.73	3.843%	$56.8333	$56.83	$56.85	$56.80
Purchase #6	$57.68	6.170%	$61.2389	$61.24	$61.25	$61.20
Purchase #7	$105.51	9.312%	$115.3351	$115.34	$115.35	$115.30
7 purchase totals =	$579.06		$621.8152	$621.81	$621.80	$621.70