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	$84.46	7.627%	$90.9018	$90.90	$90.90	$90.90
Purchase #2	$194.37	5.662%	$205.3752	$205.38	$205.40	$205.40
Purchase #3	$217.55	7.115%	$233.0287	$233.03	$233.05	$233.00
Purchase #4	$108.93	5.223%	$114.6194	$114.62	$114.60	$114.60
Purchase #5	$245.43	10.342%	$270.8124	$270.81	$270.80	$270.80
Purchase #6	$79.63	11.607%	$88.8727	$88.87	$88.85	$88.90
Purchase #7	$79.71	7.116%	$85.3822	$85.38	$85.40	$85.40
7 purchase totals =	$1,010.08		$1,088.9924	$1,088.99	$1,089.00	$1,089.00