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	$13.57	13.405%	$15.3891	$15.39	$15.40	$15.40
Purchase #2	$47.45	11.689%	$52.9964	$53.00	$53.00	$53.00
Purchase #3	$59.86	8.675%	$65.0529	$65.05	$65.05	$65.10
Purchase #4	$235.41	6.563%	$250.86	$250.86	$250.85	$250.90
Purchase #5	$18.70	8.775%	$20.3409	$20.34	$20.35	$20.30
Purchase #6	$105.90	11.332%	$117.9006	$117.90	$117.90	$117.90
Purchase #7	$142.55	12.501%	$160.3702	$160.37	$160.35	$160.40
7 purchase totals =	$623.44		$682.9101	$682.91	$682.90	$683.00