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	$41.36	3.280%	$42.7166	$42.72	$42.70	$42.70
Purchase #2	$100.62	10.450%	$111.1348	$111.13	$111.15	$111.10
Purchase #3	$59.69	10.562%	$65.9945	$65.99	$66.00	$66.00
Purchase #4	$221.82	4.119%	$230.9568	$230.96	$230.95	$231.00
Purchase #5	$20.90	7.842%	$22.539	$22.54	$22.55	$22.50
Purchase #6	$218.74	8.175%	$236.622	$236.62	$236.60	$236.60
Purchase #7	$75.65	9.514%	$82.8473	$82.85	$82.85	$82.80
7 purchase totals =	$738.78		$792.8110	$792.81	$792.80	$792.70