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	$28.40	11.695%	$31.7214	$31.72	$31.70	$31.70
Purchase #2	$18.90	13.325%	$21.4184	$21.42	$21.40	$21.40
Purchase #3	$68.55	7.693%	$73.8236	$73.82	$73.80	$73.80
Purchase #4	$163.26	3.299%	$168.6459	$168.65	$168.65	$168.60
Purchase #5	$234.27	10.795%	$259.5594	$259.56	$259.55	$259.60
Purchase #6	$62.40	4.440%	$65.1706	$65.17	$65.15	$65.20
Purchase #7	$50.39	6.375%	$53.6024	$53.60	$53.60	$53.60
7 purchase totals =	$626.17		$673.9417	$673.94	$673.85	$673.90