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	$164.96	4.540%	$172.4492	$172.45	$172.45	$172.40
Purchase #2	$201.30	8.108%	$217.6214	$217.62	$217.60	$217.60
Purchase #3	$193.70	9.341%	$211.7935	$211.79	$211.80	$211.80
Purchase #4	$116.41	10.238%	$128.3281	$128.33	$128.35	$128.30
Purchase #5	$39.87	6.810%	$42.5851	$42.59	$42.60	$42.60
Purchase #6	$61.73	4.614%	$64.5782	$64.58	$64.60	$64.60
Purchase #7	$80.50	12.360%	$90.4498	$90.45	$90.45	$90.40
7 purchase totals =	$858.47		$927.8053	$927.81	$927.85	$927.70