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	$17.49	5.192%	$18.3981	$18.40	$18.40	$18.40
Purchase #2	$196.56	13.486%	$223.0681	$223.07	$223.05	$223.10
Purchase #3	$28.38	7.768%	$30.5846	$30.58	$30.60	$30.60
Purchase #4	$36.92	12.634%	$41.5845	$41.58	$41.60	$41.60
Purchase #5	$65.68	11.104%	$72.9731	$72.97	$72.95	$73.00
Purchase #6	$99.32	4.493%	$103.7824	$103.78	$103.80	$103.80
Purchase #7	$30.99	4.315%	$32.3272	$32.33	$32.35	$32.30
7 purchase totals =	$475.34		$522.7180	$522.71	$522.75	$522.80