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	$250.78	3.384%	$259.2664	$259.27	$259.25	$259.30
Purchase #2	$136.61	10.440%	$150.8721	$150.87	$150.85	$150.90
Purchase #3	$50.96	4.498%	$53.2522	$53.25	$53.25	$53.30
Purchase #4	$116.65	11.551%	$130.1242	$130.12	$130.10	$130.10
Purchase #5	$175.91	9.430%	$192.4983	$192.50	$192.50	$192.50
Purchase #6	$127.67	12.449%	$143.5636	$143.56	$143.55	$143.60
Purchase #7	$7.59	4.793%	$7.9538	$7.95	$7.95	$8.00
7 purchase totals =	$866.17		$937.5306	$937.52	$937.45	$937.70