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	$48.86	6.231%	$51.9045	$51.90	$51.90	$51.90
Purchase #2	$79.52	11.460%	$88.633	$88.63	$88.65	$88.60
Purchase #3	$61.41	11.612%	$68.5409	$68.54	$68.55	$68.50
Purchase #4	$72.60	6.620%	$77.4061	$77.41	$77.40	$77.40
Purchase #5	$145.83	7.322%	$156.5077	$156.51	$156.50	$156.50
Purchase #6	$84.75	6.509%	$90.2664	$90.27	$90.25	$90.30
Purchase #7	$124.97	4.706%	$130.8511	$130.85	$130.85	$130.90
7 purchase totals =	$617.94		$664.1097	$664.11	$664.10	$664.10