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	$102.33	6.590%	$109.0735	$109.07	$109.05	$109.10
Purchase #2	$50.42	7.175%	$54.0376	$54.04	$54.05	$54.00
Purchase #3	$98.64	6.130%	$104.6866	$104.69	$104.70	$104.70
Purchase #4	$190.47	10.747%	$210.9398	$210.94	$210.95	$210.90
Purchase #5	$79.92	8.248%	$86.5118	$86.51	$86.50	$86.50
Purchase #6	$74.84	10.762%	$82.8943	$82.89	$82.90	$82.90
Purchase #7	$116.88	4.855%	$122.5545	$122.55	$122.55	$122.60
7 purchase totals =	$713.50		$770.6981	$770.69	$770.70	$770.70