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	$230.45	5.509%	$243.1455	$243.15	$243.15	$243.10
Purchase #2	$161.28	5.871%	$170.7487	$170.75	$170.75	$170.70
Purchase #3	$71.69	10.150%	$78.9665	$78.97	$78.95	$79.00
Purchase #4	$74.44	12.102%	$83.4487	$83.45	$83.45	$83.40
Purchase #5	$76.56	12.220%	$85.9156	$85.92	$85.90	$85.90
Purchase #6	$82.94	8.676%	$90.1359	$90.14	$90.15	$90.10
Purchase #7	$77.89	5.442%	$82.1288	$82.13	$82.15	$82.10
7 purchase totals =	$775.25		$834.4897	$834.51	$834.50	$834.30