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	$33.75	6.132%	$35.8196	$35.82	$35.80	$35.80
Purchase #2	$61.39	3.598%	$63.5988	$63.60	$63.60	$63.60
Purchase #3	$20.86	13.301%	$23.6346	$23.63	$23.65	$23.60
Purchase #4	$10.86	3.580%	$11.2488	$11.25	$11.25	$11.20
Purchase #5	$52.61	8.140%	$56.8925	$56.89	$56.90	$56.90
Purchase #6	$128.61	13.770%	$146.3196	$146.32	$146.30	$146.30
Purchase #7	$196.40	3.526%	$203.3251	$203.33	$203.35	$203.30
7 purchase totals =	$504.48		$540.8390	$540.84	$540.85	$540.70