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	$79.86	7.340%	$85.7217	$85.72	$85.70	$85.70
Purchase #2	$170.32	6.404%	$181.2273	$181.23	$181.25	$181.20
Purchase #3	$140.87	3.847%	$146.2893	$146.29	$146.30	$146.30
Purchase #4	$164.47	8.488%	$178.4302	$178.43	$178.45	$178.40
Purchase #5	$94.50	9.860%	$103.8177	$103.82	$103.80	$103.80
Purchase #6	$96.72	10.212%	$106.597	$106.60	$106.60	$106.60
Purchase #7	$33.74	5.728%	$35.6726	$35.67	$35.65	$35.70
7 purchase totals =	$780.48		$837.7558	$837.76	$837.75	$837.70