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	$181.34	10.174%	$199.7895	$199.79	$199.80	$199.80
Purchase #2	$66.92	4.730%	$70.0853	$70.09	$70.10	$70.10
Purchase #3	$59.66	5.490%	$62.9353	$62.94	$62.95	$62.90
Purchase #4	$88.46	9.128%	$96.5346	$96.53	$96.55	$96.50
Purchase #5	$72.98	7.637%	$78.5535	$78.55	$78.55	$78.60
Purchase #6	$91.51	5.404%	$96.4552	$96.46	$96.45	$96.50
Purchase #7	$39.80	5.492%	$41.9858	$41.99	$42.00	$42.00
7 purchase totals =	$600.67		$646.3392	$646.35	$646.40	$646.40