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	$105.88	8.253%	$114.6183	$114.62	$114.60	$114.60
Purchase #2	$98.45	12.143%	$110.4048	$110.40	$110.40	$110.40
Purchase #3	$118.95	7.516%	$127.8903	$127.89	$127.90	$127.90
Purchase #4	$53.96	9.526%	$59.1002	$59.10	$59.10	$59.10
Purchase #5	$21.69	8.539%	$23.5421	$23.54	$23.55	$23.50
Purchase #6	$119.36	12.291%	$134.0305	$134.03	$134.05	$134.00
Purchase #7	$31.76	13.788%	$36.1391	$36.14	$36.15	$36.10
7 purchase totals =	$550.05		$605.7253	$605.72	$605.75	$605.60