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	$108.91	5.207%	$114.5809	$114.58	$114.60	$114.60
Purchase #2	$193.37	9.292%	$211.3379	$211.34	$211.35	$211.30
Purchase #3	$229.50	11.548%	$256.0027	$256.00	$256.00	$256.00
Purchase #4	$19.91	8.574%	$21.6171	$21.62	$21.60	$21.60
Purchase #5	$30.56	11.673%	$34.1273	$34.13	$34.15	$34.10
Purchase #6	$33.39	12.488%	$37.5597	$37.56	$37.55	$37.60
Purchase #7	$157.70	9.443%	$172.5916	$172.59	$172.60	$172.60
7 purchase totals =	$773.34		$847.8172	$847.82	$847.85	$847.80