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	$158.34	3.649%	$164.1178	$164.12	$164.10	$164.10
Purchase #2	$120.25	10.301%	$132.637	$132.64	$132.65	$132.60
Purchase #3	$132.57	6.308%	$140.9325	$140.93	$140.95	$140.90
Purchase #4	$143.64	5.692%	$151.816	$151.82	$151.80	$151.80
Purchase #5	$191.53	11.174%	$212.9316	$212.93	$212.95	$212.90
Purchase #6	$130.87	13.467%	$148.4943	$148.49	$148.50	$148.50
Purchase #7	$217.30	9.729%	$238.4411	$238.44	$238.45	$238.40
7 purchase totals =	$1,094.50		$1,189.3703	$1,189.37	$1,189.40	$1,189.20