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	$96.36	4.109%	$100.3194	$100.32	$100.30	$100.30
Purchase #2	$104.77	4.617%	$109.6072	$109.61	$109.60	$109.60
Purchase #3	$34.57	6.194%	$36.7113	$36.71	$36.70	$36.70
Purchase #4	$94.31	10.784%	$104.4804	$104.48	$104.50	$104.50
Purchase #5	$164.43	11.485%	$183.3148	$183.31	$183.30	$183.30
Purchase #6	$200.35	9.324%	$219.0306	$219.03	$219.05	$219.00
Purchase #7	$39.48	11.117%	$43.869	$43.87	$43.85	$43.90
7 purchase totals =	$734.27		$797.3327	$797.33	$797.30	$797.30