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	$54.86	4.825%	$57.507	$57.51	$57.50	$57.50
Purchase #2	$62.38	9.169%	$68.0996	$68.10	$68.10	$68.10
Purchase #3	$62.53	6.376%	$66.5169	$66.52	$66.50	$66.50
Purchase #4	$127.44	10.454%	$140.7626	$140.76	$140.75	$140.80
Purchase #5	$28.33	11.666%	$31.635	$31.64	$31.65	$31.60
Purchase #6	$65.38	7.516%	$70.294	$70.29	$70.30	$70.30
Purchase #7	$155.68	4.143%	$162.1298	$162.13	$162.15	$162.10
7 purchase totals =	$556.60		$596.9449	$596.95	$596.95	$596.90