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	$26.73	11.772%	$29.8767	$29.88	$29.90	$29.90
Purchase #2	$159.89	3.450%	$165.4062	$165.41	$165.40	$165.40
Purchase #3	$73.89	11.705%	$82.5388	$82.54	$82.55	$82.50
Purchase #4	$10.36	9.586%	$11.3531	$11.35	$11.35	$11.40
Purchase #5	$9.70	4.515%	$10.138	$10.14	$10.15	$10.10
Purchase #6	$235.92	12.570%	$265.5751	$265.58	$265.60	$265.60
Purchase #7	$196.70	13.550%	$223.3529	$223.35	$223.35	$223.40
7 purchase totals =	$713.19		$788.2408	$788.25	$788.30	$788.30