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	$124.55	5.654%	$131.5921	$131.59	$131.60	$131.60
Purchase #2	$11.41	12.183%	$12.8001	$12.80	$12.80	$12.80
Purchase #3	$81.25	9.671%	$89.1077	$89.11	$89.10	$89.10
Purchase #4	$217.95	5.461%	$229.8522	$229.85	$229.85	$229.90
Purchase #5	$220.58	7.759%	$237.6948	$237.69	$237.70	$237.70
Purchase #6	$10.35	3.744%	$10.7375	$10.74	$10.75	$10.70
Purchase #7	$69.73	12.657%	$78.5557	$78.56	$78.55	$78.60
7 purchase totals =	$735.82		$790.3401	$790.34	$790.35	$790.40