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	$40.28	5.711%	$42.5804	$42.58	$42.60	$42.60
Purchase #2	$135.61	9.518%	$148.5174	$148.52	$148.50	$148.50
Purchase #3	$103.84	10.643%	$114.8917	$114.89	$114.90	$114.90
Purchase #4	$233.85	3.589%	$242.2429	$242.24	$242.25	$242.20
Purchase #5	$190.98	6.376%	$203.1569	$203.16	$203.15	$203.20
Purchase #6	$92.51	8.218%	$100.1125	$100.11	$100.10	$100.10
Purchase #7	$90.47	6.405%	$96.2646	$96.26	$96.25	$96.30
7 purchase totals =	$887.54		$947.7664	$947.76	$947.75	$947.80