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	$19.89	3.531%	$20.5923	$20.59	$20.60	$20.60
Purchase #2	$127.84	3.763%	$132.6506	$132.65	$132.65	$132.70
Purchase #3	$69.48	3.444%	$71.8729	$71.87	$71.85	$71.90
Purchase #4	$73.98	11.189%	$82.2576	$82.26	$82.25	$82.30
Purchase #5	$29.85	12.732%	$33.6505	$33.65	$33.65	$33.70
Purchase #6	$107.26	6.409%	$114.1343	$114.13	$114.15	$114.10
Purchase #7	$92.62	4.646%	$96.9231	$96.92	$96.90	$96.90
7 purchase totals =	$520.92		$552.0813	$552.07	$552.05	$552.20