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	$86.28	6.649%	$92.0168	$92.02	$92.00	$92.00
Purchase #2	$147.66	9.594%	$161.8265	$161.83	$161.85	$161.80
Purchase #3	$92.77	8.111%	$100.2946	$100.29	$100.30	$100.30
Purchase #4	$126.89	11.864%	$141.9442	$141.94	$141.95	$141.90
Purchase #5	$167.90	9.286%	$183.4912	$183.49	$183.50	$183.50
Purchase #6	$185.49	13.273%	$210.1101	$210.11	$210.10	$210.10
Purchase #7	$89.90	12.790%	$101.3982	$101.40	$101.40	$101.40
7 purchase totals =	$896.89		$991.0816	$991.08	$991.10	$991.00