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	$136.82	3.584%	$141.7236	$141.72	$141.70	$141.70
Purchase #2	$191.54	6.726%	$204.423	$204.42	$204.40	$204.40
Purchase #3	$135.66	4.786%	$142.1527	$142.15	$142.15	$142.20
Purchase #4	$182.86	3.146%	$188.6128	$188.61	$188.60	$188.60
Purchase #5	$23.89	5.603%	$25.2286	$25.23	$25.25	$25.20
Purchase #6	$142.85	13.783%	$162.539	$162.54	$162.55	$162.50
Purchase #7	$105.48	5.297%	$111.0673	$111.07	$111.05	$111.10
7 purchase totals =	$919.10		$975.7470	$975.74	$975.70	$975.70