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	$65.73	11.839%	$73.5118	$73.51	$73.50	$73.50
Purchase #2	$204.67	13.872%	$233.0618	$233.06	$233.05	$233.10
Purchase #3	$99.83	3.187%	$103.0116	$103.01	$103.00	$103.00
Purchase #4	$116.56	5.810%	$123.3321	$123.33	$123.35	$123.30
Purchase #5	$183.91	9.256%	$200.9327	$200.93	$200.95	$200.90
Purchase #6	$43.92	10.559%	$48.5575	$48.56	$48.55	$48.60
Purchase #7	$119.55	9.182%	$130.5271	$130.53	$130.55	$130.50
7 purchase totals =	$834.17		$912.9346	$912.93	$912.95	$912.90