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	$50.73	6.505%	$54.03	$54.03	$54.05	$54.00
Purchase #2	$222.97	12.740%	$251.3764	$251.38	$251.40	$251.40
Purchase #3	$19.25	9.827%	$21.1417	$21.14	$21.15	$21.10
Purchase #4	$32.29	5.518%	$34.0718	$34.07	$34.05	$34.10
Purchase #5	$50.72	7.118%	$54.3302	$54.33	$54.35	$54.30
Purchase #6	$246.65	6.834%	$263.5061	$263.51	$263.50	$263.50
Purchase #7	$31.30	4.812%	$32.8062	$32.81	$32.80	$32.80
7 purchase totals =	$653.91		$711.2624	$711.27	$711.30	$711.20