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	$235.61	6.290%	$250.4299	$250.43	$250.45	$250.40
Purchase #2	$132.78	12.194%	$148.9712	$148.97	$148.95	$149.00
Purchase #3	$134.54	13.427%	$152.6047	$152.60	$152.60	$152.60
Purchase #4	$72.87	10.729%	$80.6882	$80.69	$80.70	$80.70
Purchase #5	$140.32	3.255%	$144.8874	$144.89	$144.90	$144.90
Purchase #6	$199.33	11.632%	$222.5161	$222.52	$222.50	$222.50
Purchase #7	$148.91	7.423%	$159.9636	$159.96	$159.95	$160.00
7 purchase totals =	$1,064.36		$1,160.0611	$1,160.06	$1,160.05	$1,160.10