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	$211.71	13.436%	$240.1554	$240.16	$240.15	$240.20
Purchase #2	$93.89	12.795%	$105.9032	$105.90	$105.90	$105.90
Purchase #3	$100.48	12.798%	$113.3394	$113.34	$113.35	$113.30
Purchase #4	$209.85	6.391%	$223.2615	$223.26	$223.25	$223.30
Purchase #5	$18.77	11.395%	$20.9088	$20.91	$20.90	$20.90
Purchase #6	$67.91	9.373%	$74.2752	$74.28	$74.30	$74.30
Purchase #7	$107.93	8.290%	$116.8774	$116.88	$116.90	$116.90
7 purchase totals =	$810.54		$894.7209	$894.73	$894.75	$894.80