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	$37.80	11.702%	$42.2234	$42.22	$42.20	$42.20
Purchase #2	$61.75	5.865%	$65.3716	$65.37	$65.35	$65.40
Purchase #3	$249.37	13.534%	$283.1197	$283.12	$283.10	$283.10
Purchase #4	$76.58	3.359%	$79.1523	$79.15	$79.15	$79.20
Purchase #5	$179.62	9.628%	$196.9138	$196.91	$196.90	$196.90
Purchase #6	$176.42	9.111%	$192.4936	$192.49	$192.50	$192.50
Purchase #7	$134.28	4.304%	$140.0594	$140.06	$140.05	$140.10
7 purchase totals =	$915.82		$999.3338	$999.32	$999.25	$999.40