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	$123.42	11.271%	$137.3307	$137.33	$137.35	$137.30
Purchase #2	$227.32	8.348%	$246.2967	$246.30	$246.30	$246.30
Purchase #3	$224.61	3.834%	$233.2215	$233.22	$233.20	$233.20
Purchase #4	$137.49	4.507%	$143.6867	$143.69	$143.70	$143.70
Purchase #5	$183.85	6.567%	$195.9234	$195.92	$195.90	$195.90
Purchase #6	$241.87	7.824%	$260.7939	$260.79	$260.80	$260.80
Purchase #7	$80.49	3.865%	$83.6009	$83.60	$83.60	$83.60
7 purchase totals =	$1,219.05		$1,300.8538	$1,300.85	$1,300.85	$1,300.80