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	$18.88	6.557%	$20.118	$20.12	$20.10	$20.10
Purchase #2	$52.28	13.702%	$59.4434	$59.44	$59.45	$59.40
Purchase #3	$178.35	12.122%	$199.9696	$199.97	$199.95	$200.00
Purchase #4	$99.45	12.203%	$111.5859	$111.59	$111.60	$111.60
Purchase #5	$163.52	5.147%	$171.9364	$171.94	$171.95	$171.90
Purchase #6	$14.52	13.458%	$16.4741	$16.47	$16.45	$16.50
Purchase #7	$77.95	6.343%	$82.8944	$82.89	$82.90	$82.90
7 purchase totals =	$604.95		$662.4218	$662.42	$662.40	$662.40