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	$63.67	6.629%	$67.8907	$67.89	$67.90	$67.90
Purchase #2	$75.86	12.593%	$85.413	$85.41	$85.40	$85.40
Purchase #3	$193.80	11.507%	$216.1006	$216.10	$216.10	$216.10
Purchase #4	$67.88	6.514%	$72.3017	$72.30	$72.30	$72.30
Purchase #5	$118.94	12.355%	$133.635	$133.64	$133.65	$133.60
Purchase #6	$25.45	8.419%	$27.5926	$27.59	$27.60	$27.60
Purchase #7	$214.31	8.723%	$233.0043	$233.00	$233.00	$233.00
7 purchase totals =	$759.91		$835.9379	$835.93	$835.95	$835.90