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	$50.46	12.693%	$56.8649	$56.86	$56.85	$56.90
Purchase #2	$218.26	9.268%	$238.4883	$238.49	$238.50	$238.50
Purchase #3	$53.62	10.517%	$59.2592	$59.26	$59.25	$59.30
Purchase #4	$140.80	9.459%	$154.1183	$154.12	$154.10	$154.10
Purchase #5	$37.76	7.772%	$40.6947	$40.69	$40.70	$40.70
Purchase #6	$69.52	4.498%	$72.647	$72.65	$72.65	$72.60
Purchase #7	$14.57	12.832%	$16.4396	$16.44	$16.45	$16.40
7 purchase totals =	$584.99		$638.5120	$638.51	$638.50	$638.50