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	$45.92	10.168%	$50.5891	$50.59	$50.60	$50.60
Purchase #2	$199.57	6.182%	$211.9074	$211.91	$211.90	$211.90
Purchase #3	$133.87	12.670%	$150.8313	$150.83	$150.85	$150.80
Purchase #4	$91.70	3.252%	$94.6821	$94.68	$94.70	$94.70
Purchase #5	$93.59	7.255%	$100.38	$100.38	$100.40	$100.40
Purchase #6	$57.88	10.744%	$64.0986	$64.10	$64.10	$64.10
Purchase #7	$191.80	13.413%	$217.5261	$217.53	$217.55	$217.50
7 purchase totals =	$814.33		$890.0146	$890.02	$890.10	$890.00