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	$172.50	6.157%	$183.1208	$183.12	$183.10	$183.10
Purchase #2	$20.34	12.141%	$22.8095	$22.81	$22.80	$22.80
Purchase #3	$188.86	4.870%	$198.0575	$198.06	$198.05	$198.10
Purchase #4	$147.50	10.246%	$162.6129	$162.61	$162.60	$162.60
Purchase #5	$112.40	12.578%	$126.5377	$126.54	$126.55	$126.50
Purchase #6	$189.42	5.331%	$199.518	$199.52	$199.50	$199.50
Purchase #7	$73.90	5.679%	$78.0968	$78.10	$78.10	$78.10
7 purchase totals =	$904.92		$970.7532	$970.76	$970.70	$970.70