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	$26.59	4.264%	$27.7238	$27.72	$27.70	$27.70
Purchase #2	$23.73	3.304%	$24.514	$24.51	$24.50	$24.50
Purchase #3	$133.40	11.557%	$148.817	$148.82	$148.80	$148.80
Purchase #4	$41.73	8.259%	$45.1765	$45.18	$45.20	$45.20
Purchase #5	$158.72	3.638%	$164.4942	$164.49	$164.50	$164.50
Purchase #6	$89.87	8.646%	$97.6402	$97.64	$97.65	$97.60
Purchase #7	$6.62	9.185%	$7.228	$7.23	$7.25	$7.20
7 purchase totals =	$480.66		$515.5937	$515.59	$515.60	$515.50