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	$172.32	6.494%	$183.5105	$183.51	$183.50	$183.50
Purchase #2	$244.81	4.810%	$256.5854	$256.59	$256.60	$256.60
Purchase #3	$172.49	11.153%	$191.7278	$191.73	$191.75	$191.70
Purchase #4	$109.76	12.371%	$123.3384	$123.34	$123.35	$123.30
Purchase #5	$61.82	13.676%	$70.2745	$70.27	$70.25	$70.30
Purchase #6	$88.76	4.173%	$92.464	$92.46	$92.45	$92.50
Purchase #7	$226.62	12.744%	$255.5005	$255.50	$255.50	$255.50
7 purchase totals =	$1,076.58		$1,173.4011	$1,173.40	$1,173.40	$1,173.40