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	$5.58	13.872%	$6.3541	$6.35	$6.35	$6.40
Purchase #2	$156.70	12.414%	$176.1527	$176.15	$176.15	$176.20
Purchase #3	$59.61	5.653%	$62.9798	$62.98	$63.00	$63.00
Purchase #4	$99.75	4.502%	$104.2407	$104.24	$104.25	$104.20
Purchase #5	$181.31	5.809%	$191.8423	$191.84	$191.85	$191.80
Purchase #6	$66.77	8.468%	$72.4241	$72.42	$72.40	$72.40
Purchase #7	$160.85	9.316%	$175.8348	$175.83	$175.85	$175.80
7 purchase totals =	$730.57		$789.8285	$789.81	$789.85	$789.80