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	$153.48	4.181%	$159.897	$159.90	$159.90	$159.90
Purchase #2	$136.97	10.707%	$151.6354	$151.64	$151.65	$151.60
Purchase #3	$175.74	4.478%	$183.6096	$183.61	$183.60	$183.60
Purchase #4	$234.80	7.175%	$251.6469	$251.65	$251.65	$251.60
Purchase #5	$39.60	7.581%	$42.6021	$42.60	$42.60	$42.60
Purchase #6	$71.84	12.204%	$80.6074	$80.61	$80.60	$80.60
Purchase #7	$91.66	7.258%	$98.3127	$98.31	$98.30	$98.30
7 purchase totals =	$904.09		$968.3111	$968.32	$968.30	$968.20