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	$40.36	5.585%	$42.6141	$42.61	$42.60	$42.60
Purchase #2	$17.83	7.317%	$19.1346	$19.13	$19.15	$19.10
Purchase #3	$81.90	4.725%	$85.7698	$85.77	$85.75	$85.80
Purchase #4	$248.86	8.104%	$269.0276	$269.03	$269.05	$269.00
Purchase #5	$101.53	4.323%	$105.9191	$105.92	$105.90	$105.90
Purchase #6	$244.86	8.401%	$265.4307	$265.43	$265.45	$265.40
Purchase #7	$127.64	11.234%	$141.9791	$141.98	$142.00	$142.00
7 purchase totals =	$862.98		$929.8750	$929.87	$929.90	$929.80