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	$15.78	9.354%	$17.2561	$17.26	$17.25	$17.30
Purchase #2	$56.80	7.746%	$61.1997	$61.20	$61.20	$61.20
Purchase #3	$100.91	10.153%	$111.1554	$111.16	$111.15	$111.20
Purchase #4	$195.39	11.819%	$218.4831	$218.48	$218.50	$218.50
Purchase #5	$82.96	9.635%	$90.9532	$90.95	$90.95	$91.00
Purchase #6	$52.89	9.289%	$57.803	$57.80	$57.80	$57.80
Purchase #7	$111.64	4.469%	$116.6292	$116.63	$116.65	$116.60
7 purchase totals =	$616.37		$673.4797	$673.48	$673.50	$673.60