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	$133.87	6.526%	$142.6064	$142.61	$142.60	$142.60
Purchase #2	$227.90	11.320%	$253.6983	$253.70	$253.70	$253.70
Purchase #3	$172.61	10.382%	$190.5304	$190.53	$190.55	$190.50
Purchase #4	$100.57	10.621%	$111.2515	$111.25	$111.25	$111.30
Purchase #5	$64.69	7.764%	$69.7125	$69.71	$69.70	$69.70
Purchase #6	$198.90	13.341%	$225.4352	$225.44	$225.45	$225.40
Purchase #7	$77.56	7.110%	$83.0745	$83.07	$83.05	$83.10
7 purchase totals =	$976.10		$1,076.3088	$1,076.31	$1,076.30	$1,076.30