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	$153.56	4.523%	$160.5055	$160.51	$160.50	$160.50
Purchase #2	$106.59	7.745%	$114.8454	$114.85	$114.85	$114.80
Purchase #3	$74.82	10.183%	$82.4389	$82.44	$82.45	$82.40
Purchase #4	$194.32	13.154%	$219.8809	$219.88	$219.90	$219.90
Purchase #5	$48.80	6.279%	$51.8642	$51.86	$51.85	$51.90
Purchase #6	$80.87	5.373%	$85.2151	$85.22	$85.20	$85.20
Purchase #7	$235.55	13.285%	$266.8428	$266.84	$266.85	$266.80
7 purchase totals =	$894.51		$981.5928	$981.60	$981.60	$981.50