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	$52.98	4.781%	$55.513	$55.51	$55.50	$55.50
Purchase #2	$115.83	5.457%	$122.1508	$122.15	$122.15	$122.20
Purchase #3	$130.54	6.795%	$139.4102	$139.41	$139.40	$139.40
Purchase #4	$33.93	12.541%	$38.1852	$38.19	$38.20	$38.20
Purchase #5	$34.27	8.172%	$37.0705	$37.07	$37.05	$37.10
Purchase #6	$152.56	6.794%	$162.9249	$162.92	$162.90	$162.90
Purchase #7	$59.56	11.391%	$66.3445	$66.34	$66.35	$66.30
7 purchase totals =	$579.67		$621.5991	$621.59	$621.55	$621.60