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	$28.77	3.830%	$29.8719	$29.87	$29.85	$29.90
Purchase #2	$71.95	4.379%	$75.1007	$75.10	$75.10	$75.10
Purchase #3	$52.98	5.118%	$55.6915	$55.69	$55.70	$55.70
Purchase #4	$101.96	3.547%	$105.5765	$105.58	$105.60	$105.60
Purchase #5	$172.52	11.450%	$192.2735	$192.27	$192.25	$192.30
Purchase #6	$123.27	13.815%	$140.2998	$140.30	$140.30	$140.30
Purchase #7	$72.73	13.817%	$82.7791	$82.78	$82.80	$82.80
7 purchase totals =	$624.18		$681.5930	$681.59	$681.60	$681.70