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	$41.82	10.309%	$46.1312	$46.13	$46.15	$46.10
Purchase #2	$100.45	11.323%	$111.824	$111.82	$111.80	$111.80
Purchase #3	$142.52	5.414%	$150.236	$150.24	$150.25	$150.20
Purchase #4	$131.96	9.681%	$144.735	$144.74	$144.75	$144.70
Purchase #5	$54.38	9.182%	$59.3732	$59.37	$59.35	$59.40
Purchase #6	$226.64	12.672%	$255.3598	$255.36	$255.35	$255.40
Purchase #7	$50.41	6.214%	$53.5425	$53.54	$53.55	$53.50
7 purchase totals =	$748.18		$821.2017	$821.20	$821.20	$821.10