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	$16.64	13.139%	$18.8263	$18.83	$18.85	$18.80
Purchase #2	$69.71	11.756%	$77.9051	$77.91	$77.90	$77.90
Purchase #3	$203.51	3.324%	$210.2747	$210.27	$210.25	$210.30
Purchase #4	$152.44	6.182%	$161.8638	$161.86	$161.85	$161.90
Purchase #5	$170.74	4.760%	$178.8672	$178.87	$178.85	$178.90
Purchase #6	$202.73	4.547%	$211.9481	$211.95	$211.95	$211.90
Purchase #7	$132.78	7.406%	$142.6137	$142.61	$142.60	$142.60
7 purchase totals =	$948.55		$1,002.2989	$1,002.30	$1,002.25	$1,002.30