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	$65.30	6.123%	$69.2983	$69.30	$69.30	$69.30
Purchase #2	$100.43	11.166%	$111.644	$111.64	$111.65	$111.60
Purchase #3	$235.27	7.796%	$253.6116	$253.61	$253.60	$253.60
Purchase #4	$78.79	4.497%	$82.3332	$82.33	$82.35	$82.30
Purchase #5	$219.54	9.542%	$240.4885	$240.49	$240.50	$240.50
Purchase #6	$177.58	8.613%	$192.875	$192.88	$192.90	$192.90
Purchase #7	$30.30	7.454%	$32.5586	$32.56	$32.55	$32.60
7 purchase totals =	$907.21		$982.8092	$982.81	$982.85	$982.80