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	$25.70	12.340%	$28.8714	$28.87	$28.85	$28.90
Purchase #2	$108.44	9.327%	$118.5542	$118.55	$118.55	$118.60
Purchase #3	$71.39	11.304%	$79.4599	$79.46	$79.45	$79.50
Purchase #4	$35.92	10.780%	$39.7922	$39.79	$39.80	$39.80
Purchase #5	$135.98	5.204%	$143.0564	$143.06	$143.05	$143.10
Purchase #6	$33.91	10.808%	$37.575	$37.58	$37.60	$37.60
Purchase #7	$29.69	6.235%	$31.5412	$31.54	$31.55	$31.50
7 purchase totals =	$441.03		$478.8503	$478.85	$478.85	$479.00