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	$100.33	11.793%	$112.1619	$112.16	$112.15	$112.20
Purchase #2	$81.95	9.203%	$89.4919	$89.49	$89.50	$89.50
Purchase #3	$168.85	6.511%	$179.8438	$179.84	$179.85	$179.80
Purchase #4	$141.41	12.352%	$158.877	$158.88	$158.90	$158.90
Purchase #5	$135.44	10.438%	$149.5772	$149.58	$149.60	$149.60
Purchase #6	$49.59	13.527%	$56.298	$56.30	$56.30	$56.30
Purchase #7	$172.82	8.268%	$187.1088	$187.11	$187.10	$187.10
7 purchase totals =	$850.39		$933.3586	$933.36	$933.40	$933.40