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	$199.86	10.732%	$221.309	$221.31	$221.30	$221.30
Purchase #2	$126.59	5.415%	$133.4448	$133.44	$133.45	$133.40
Purchase #3	$100.73	4.695%	$105.4593	$105.46	$105.45	$105.50
Purchase #4	$249.42	9.295%	$272.6036	$272.60	$272.60	$272.60
Purchase #5	$55.79	12.494%	$62.7604	$62.76	$62.75	$62.80
Purchase #6	$79.97	10.508%	$88.3732	$88.37	$88.35	$88.40
Purchase #7	$115.89	4.827%	$121.484	$121.48	$121.50	$121.50
7 purchase totals =	$928.25		$1,005.4343	$1,005.42	$1,005.40	$1,005.50