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	$210.72	6.218%	$223.8226	$223.82	$223.80	$223.80
Purchase #2	$199.34	13.500%	$226.2509	$226.25	$226.25	$226.30
Purchase #3	$57.94	12.197%	$65.0069	$65.01	$65.00	$65.00
Purchase #4	$99.25	4.509%	$103.7252	$103.73	$103.75	$103.70
Purchase #5	$89.31	7.848%	$96.319	$96.32	$96.30	$96.30
Purchase #6	$206.42	10.392%	$227.8712	$227.87	$227.85	$227.90
Purchase #7	$69.30	9.411%	$75.8218	$75.82	$75.80	$75.80
7 purchase totals =	$932.28		$1,018.8176	$1,018.82	$1,018.75	$1,018.80