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	$223.44	10.687%	$247.319	$247.32	$247.30	$247.30
Purchase #2	$82.48	8.845%	$89.7754	$89.78	$89.80	$89.80
Purchase #3	$240.73	5.762%	$254.6009	$254.60	$254.60	$254.60
Purchase #4	$46.58	13.625%	$52.9265	$52.93	$52.95	$52.90
Purchase #5	$91.55	8.529%	$99.3583	$99.36	$99.35	$99.40
Purchase #6	$64.69	4.346%	$67.5014	$67.50	$67.50	$67.50
Purchase #7	$156.45	9.781%	$171.7524	$171.75	$171.75	$171.80
7 purchase totals =	$905.92		$983.2339	$983.24	$983.25	$983.30