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	$93.98	6.596%	$100.1789	$100.18	$100.20	$100.20
Purchase #2	$100.98	4.147%	$105.1676	$105.17	$105.15	$105.20
Purchase #3	$67.95	3.707%	$70.4689	$70.47	$70.45	$70.50
Purchase #4	$100.98	12.661%	$113.7651	$113.77	$113.75	$113.80
Purchase #5	$38.67	7.460%	$41.5548	$41.55	$41.55	$41.60
Purchase #6	$34.77	7.293%	$37.3058	$37.31	$37.30	$37.30
Purchase #7	$69.55	3.480%	$71.9703	$71.97	$71.95	$72.00
7 purchase totals =	$506.88		$540.4114	$540.42	$540.35	$540.60