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	$170.39	13.155%	$192.8048	$192.80	$192.80	$192.80
Purchase #2	$105.27	4.382%	$109.8829	$109.88	$109.90	$109.90
Purchase #3	$150.76	9.589%	$165.2164	$165.22	$165.20	$165.20
Purchase #4	$80.78	5.655%	$85.3481	$85.35	$85.35	$85.30
Purchase #5	$41.50	3.173%	$42.8168	$42.82	$42.80	$42.80
Purchase #6	$8.54	11.348%	$9.5091	$9.51	$9.50	$9.50
Purchase #7	$171.90	6.864%	$183.6992	$183.70	$183.70	$183.70
7 purchase totals =	$729.14		$789.2773	$789.28	$789.25	$789.20