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	$70.83	3.186%	$73.0866	$73.09	$73.10	$73.10
Purchase #2	$218.82	13.433%	$248.2141	$248.21	$248.20	$248.20
Purchase #3	$218.60	9.248%	$238.8161	$238.82	$238.80	$238.80
Purchase #4	$61.76	6.204%	$65.5916	$65.59	$65.60	$65.60
Purchase #5	$58.38	11.193%	$64.9145	$64.91	$64.90	$64.90
Purchase #6	$100.94	10.803%	$111.8445	$111.84	$111.85	$111.80
Purchase #7	$103.47	5.356%	$109.0119	$109.01	$109.00	$109.00
7 purchase totals =	$832.80		$911.4793	$911.47	$911.45	$911.40