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	$101.31	5.317%	$106.6967	$106.70	$106.70	$106.70
Purchase #2	$57.39	5.840%	$60.7416	$60.74	$60.75	$60.70
Purchase #3	$21.73	13.433%	$24.649	$24.65	$24.65	$24.60
Purchase #4	$196.56	13.783%	$223.6519	$223.65	$223.65	$223.70
Purchase #5	$59.96	12.160%	$67.2511	$67.25	$67.25	$67.30
Purchase #6	$102.50	11.700%	$114.4925	$114.49	$114.50	$114.50
Purchase #7	$78.45	6.115%	$83.2472	$83.25	$83.25	$83.20
7 purchase totals =	$617.90		$680.7300	$680.73	$680.75	$680.70