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	$228.59	6.518%	$243.4895	$243.49	$243.50	$243.50
Purchase #2	$52.54	7.732%	$56.6024	$56.60	$56.60	$56.60
Purchase #3	$159.90	7.679%	$172.1787	$172.18	$172.20	$172.20
Purchase #4	$97.76	13.253%	$110.7161	$110.72	$110.70	$110.70
Purchase #5	$119.99	7.157%	$128.5777	$128.58	$128.60	$128.60
Purchase #6	$28.89	12.357%	$32.4599	$32.46	$32.45	$32.50
Purchase #7	$99.38	8.761%	$108.0867	$108.09	$108.10	$108.10
7 purchase totals =	$787.05		$852.1110	$852.12	$852.15	$852.20