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	$53.64	5.163%	$56.4094	$56.41	$56.40	$56.40
Purchase #2	$54.85	8.498%	$59.5112	$59.51	$59.50	$59.50
Purchase #3	$140.54	10.255%	$154.9524	$154.95	$154.95	$155.00
Purchase #4	$133.55	12.455%	$150.1837	$150.18	$150.20	$150.20
Purchase #5	$67.68	6.827%	$72.3005	$72.30	$72.30	$72.30
Purchase #6	$35.85	11.394%	$39.9347	$39.93	$39.95	$39.90
Purchase #7	$151.48	4.377%	$158.1103	$158.11	$158.10	$158.10
7 purchase totals =	$637.59		$691.4022	$691.39	$691.40	$691.40