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	$75.61	4.231%	$78.8091	$78.81	$78.80	$78.80
Purchase #2	$151.65	10.734%	$167.9281	$167.93	$167.95	$167.90
Purchase #3	$101.72	10.265%	$112.1616	$112.16	$112.15	$112.20
Purchase #4	$249.67	5.563%	$263.5591	$263.56	$263.55	$263.60
Purchase #5	$115.32	11.768%	$128.8909	$128.89	$128.90	$128.90
Purchase #6	$30.88	6.721%	$32.9554	$32.96	$32.95	$33.00
Purchase #7	$233.83	4.390%	$244.0951	$244.10	$244.10	$244.10
7 purchase totals =	$958.68		$1,028.3993	$1,028.41	$1,028.40	$1,028.50