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	$38.62	5.763%	$40.8457	$40.85	$40.85	$40.80
Purchase #2	$117.81	10.825%	$130.5629	$130.56	$130.55	$130.60
Purchase #3	$64.74	7.476%	$69.58	$69.58	$69.60	$69.60
Purchase #4	$166.32	11.780%	$185.9125	$185.91	$185.90	$185.90
Purchase #5	$5.36	12.319%	$6.0203	$6.02	$6.00	$6.00
Purchase #6	$52.58	13.498%	$59.6772	$59.68	$59.70	$59.70
Purchase #7	$65.43	3.865%	$67.9589	$67.96	$67.95	$68.00
7 purchase totals =	$510.86		$560.5575	$560.56	$560.55	$560.60