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	$132.80	13.396%	$150.5899	$150.59	$150.60	$150.60
Purchase #2	$38.33	8.832%	$41.7153	$41.72	$41.70	$41.70
Purchase #3	$241.53	7.121%	$258.7294	$258.73	$258.75	$258.70
Purchase #4	$219.27	8.370%	$237.6229	$237.62	$237.60	$237.60
Purchase #5	$103.72	11.729%	$115.8853	$115.89	$115.90	$115.90
Purchase #6	$20.82	8.167%	$22.5204	$22.52	$22.50	$22.50
Purchase #7	$68.33	5.770%	$72.2726	$72.27	$72.25	$72.30
7 purchase totals =	$824.80		$899.3358	$899.34	$899.30	$899.30