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	$16.63	12.677%	$18.7382	$18.74	$18.75	$18.70
Purchase #2	$205.64	12.505%	$231.3553	$231.36	$231.35	$231.40
Purchase #3	$222.50	4.726%	$233.0154	$233.02	$233.00	$233.00
Purchase #4	$36.30	4.222%	$37.8326	$37.83	$37.85	$37.80
Purchase #5	$115.26	11.813%	$128.8757	$128.88	$128.90	$128.90
Purchase #6	$146.90	7.585%	$158.0424	$158.04	$158.05	$158.00
Purchase #7	$129.29	9.778%	$141.932	$141.93	$141.95	$141.90
7 purchase totals =	$872.52		$949.7916	$949.80	$949.85	$949.70