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	$30.64	3.837%	$31.8157	$31.82	$31.80	$31.80
Purchase #2	$78.84	5.291%	$83.0114	$83.01	$83.00	$83.00
Purchase #3	$73.46	7.181%	$78.7352	$78.74	$78.75	$78.70
Purchase #4	$31.81	4.752%	$33.3216	$33.32	$33.30	$33.30
Purchase #5	$11.52	8.640%	$12.5153	$12.52	$12.50	$12.50
Purchase #6	$153.38	6.206%	$162.8988	$162.90	$162.90	$162.90
Purchase #7	$23.77	8.701%	$25.8382	$25.84	$25.85	$25.80
7 purchase totals =	$403.42		$428.1362	$428.15	$428.10	$428.00