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	$222.45	13.848%	$253.2549	$253.25	$253.25	$253.30
Purchase #2	$29.61	5.362%	$31.1977	$31.20	$31.20	$31.20
Purchase #3	$53.92	10.707%	$59.6932	$59.69	$59.70	$59.70
Purchase #4	$208.92	11.176%	$232.2689	$232.27	$232.25	$232.30
Purchase #5	$157.61	10.300%	$173.8438	$173.84	$173.85	$173.80
Purchase #6	$168.56	13.258%	$190.9077	$190.91	$190.90	$190.90
Purchase #7	$71.94	11.675%	$80.339	$80.34	$80.35	$80.30
7 purchase totals =	$913.01		$1,021.5052	$1,021.50	$1,021.50	$1,021.50