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	$48.50	6.266%	$51.539	$51.54	$51.55	$51.50
Purchase #2	$143.71	10.518%	$158.8254	$158.83	$158.85	$158.80
Purchase #3	$147.40	6.594%	$157.1196	$157.12	$157.10	$157.10
Purchase #4	$112.43	5.325%	$118.4169	$118.42	$118.40	$118.40
Purchase #5	$45.73	11.475%	$50.9775	$50.98	$51.00	$51.00
Purchase #6	$233.70	12.555%	$263.041	$263.04	$263.05	$263.00
Purchase #7	$245.46	8.732%	$266.8936	$266.89	$266.90	$266.90
7 purchase totals =	$976.93		$1,066.8130	$1,066.82	$1,066.85	$1,066.70