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	$107.55	3.515%	$111.3304	$111.33	$111.35	$111.30
Purchase #2	$171.78	10.789%	$190.3133	$190.31	$190.30	$190.30
Purchase #3	$58.70	4.454%	$61.3145	$61.31	$61.30	$61.30
Purchase #4	$176.82	9.249%	$193.1741	$193.17	$193.15	$193.20
Purchase #5	$60.61	8.855%	$65.977	$65.98	$66.00	$66.00
Purchase #6	$45.81	10.345%	$50.549	$50.55	$50.55	$50.50
Purchase #7	$79.94	8.567%	$86.7885	$86.79	$86.80	$86.80
7 purchase totals =	$701.21		$759.4468	$759.44	$759.45	$759.40