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	$153.73	13.293%	$174.1653	$174.17	$174.15	$174.20
Purchase #2	$36.88	7.138%	$39.5125	$39.51	$39.50	$39.50
Purchase #3	$105.53	6.770%	$112.6744	$112.67	$112.65	$112.70
Purchase #4	$165.31	11.322%	$184.0264	$184.03	$184.05	$184.00
Purchase #5	$80.73	5.867%	$85.4664	$85.47	$85.45	$85.50
Purchase #6	$49.95	4.215%	$52.0554	$52.06	$52.05	$52.10
Purchase #7	$237.89	5.437%	$250.8241	$250.82	$250.80	$250.80
7 purchase totals =	$830.02		$898.7245	$898.73	$898.65	$898.80