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	$54.76	6.708%	$58.4333	$58.43	$58.45	$58.40
Purchase #2	$139.82	11.109%	$155.3526	$155.35	$155.35	$155.40
Purchase #3	$39.90	3.727%	$41.3871	$41.39	$41.40	$41.40
Purchase #4	$29.48	10.197%	$32.4861	$32.49	$32.50	$32.50
Purchase #5	$174.27	5.732%	$184.2592	$184.26	$184.25	$184.30
Purchase #6	$174.86	4.300%	$182.379	$182.38	$182.40	$182.40
Purchase #7	$11.64	9.258%	$12.7176	$12.72	$12.70	$12.70
7 purchase totals =	$624.73		$667.0149	$667.02	$667.05	$667.10