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	$105.89	3.438%	$109.5305	$109.53	$109.55	$109.50
Purchase #2	$246.49	4.383%	$257.2937	$257.29	$257.30	$257.30
Purchase #3	$130.39	5.856%	$138.0256	$138.03	$138.05	$138.00
Purchase #4	$33.57	11.206%	$37.3319	$37.33	$37.35	$37.30
Purchase #5	$94.69	6.464%	$100.8108	$100.81	$100.80	$100.80
Purchase #6	$65.37	7.318%	$70.1538	$70.15	$70.15	$70.20
Purchase #7	$238.26	11.394%	$265.4073	$265.41	$265.40	$265.40
7 purchase totals =	$914.66		$978.5536	$978.55	$978.60	$978.50