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	$250.30	13.868%	$285.0116	$285.01	$285.00	$285.00
Purchase #2	$35.27	10.358%	$38.9233	$38.92	$38.90	$38.90
Purchase #3	$170.32	11.427%	$189.7825	$189.78	$189.80	$189.80
Purchase #4	$32.78	3.650%	$33.9765	$33.98	$34.00	$34.00
Purchase #5	$162.87	5.426%	$171.7073	$171.71	$171.70	$171.70
Purchase #6	$10.71	5.317%	$11.2795	$11.28	$11.30	$11.30
Purchase #7	$223.54	9.427%	$244.6131	$244.61	$244.60	$244.60
7 purchase totals =	$885.79		$975.2938	$975.29	$975.30	$975.30