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	$111.83	3.852%	$116.1377	$116.14	$116.15	$116.10
Purchase #2	$30.35	9.400%	$33.2029	$33.20	$33.20	$33.20
Purchase #3	$160.80	11.159%	$178.7437	$178.74	$178.75	$178.70
Purchase #4	$49.32	6.289%	$52.4217	$52.42	$52.40	$52.40
Purchase #5	$96.30	9.740%	$105.6796	$105.68	$105.70	$105.70
Purchase #6	$130.45	12.352%	$146.5632	$146.56	$146.55	$146.60
Purchase #7	$31.37	7.632%	$33.7642	$33.76	$33.75	$33.80
7 purchase totals =	$610.42		$666.5130	$666.50	$666.50	$666.50