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	$37.94	6.435%	$40.3814	$40.38	$40.40	$40.40
Purchase #2	$79.83	10.648%	$88.3303	$88.33	$88.35	$88.30
Purchase #3	$18.67	3.639%	$19.3494	$19.35	$19.35	$19.30
Purchase #4	$144.29	12.392%	$162.1704	$162.17	$162.15	$162.20
Purchase #5	$191.33	13.561%	$217.2763	$217.28	$217.30	$217.30
Purchase #6	$137.64	6.203%	$146.1778	$146.18	$146.20	$146.20
Purchase #7	$131.78	7.759%	$142.0048	$142.00	$142.00	$142.00
7 purchase totals =	$741.48		$815.6904	$815.69	$815.75	$815.70