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	$60.43	11.345%	$67.2858	$67.29	$67.30	$67.30
Purchase #2	$216.52	5.305%	$228.0064	$228.01	$228.00	$228.00
Purchase #3	$65.72	6.505%	$69.9951	$70.00	$70.00	$70.00
Purchase #4	$151.25	12.722%	$170.492	$170.49	$170.50	$170.50
Purchase #5	$83.40	3.767%	$86.5417	$86.54	$86.55	$86.50
Purchase #6	$81.98	9.627%	$89.8722	$89.87	$89.85	$89.90
Purchase #7	$107.46	9.363%	$117.5215	$117.52	$117.50	$117.50
7 purchase totals =	$766.76		$829.7147	$829.72	$829.70	$829.70