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	$235.35	4.621%	$246.2255	$246.23	$246.25	$246.20
Purchase #2	$17.88	12.244%	$20.0692	$20.07	$20.05	$20.10
Purchase #3	$93.51	11.821%	$104.5638	$104.56	$104.55	$104.60
Purchase #4	$89.46	10.856%	$99.1718	$99.17	$99.15	$99.20
Purchase #5	$37.79	6.137%	$40.1092	$40.11	$40.10	$40.10
Purchase #6	$82.25	4.703%	$86.1182	$86.12	$86.10	$86.10
Purchase #7	$9.61	6.398%	$10.2248	$10.22	$10.20	$10.20
7 purchase totals =	$565.85		$606.4825	$606.48	$606.40	$606.50