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	$100.30	5.434%	$105.7503	$105.75	$105.75	$105.80
Purchase #2	$82.60	11.230%	$91.876	$91.88	$91.90	$91.90
Purchase #3	$162.46	5.371%	$171.1857	$171.19	$171.20	$171.20
Purchase #4	$31.45	10.282%	$34.6837	$34.68	$34.70	$34.70
Purchase #5	$101.28	4.180%	$105.5135	$105.51	$105.50	$105.50
Purchase #6	$113.44	10.685%	$125.5611	$125.56	$125.55	$125.60
Purchase #7	$20.91	6.391%	$22.2464	$22.25	$22.25	$22.20
7 purchase totals =	$612.44		$656.8167	$656.82	$656.85	$656.90