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	$166.89	4.453%	$174.3216	$174.32	$174.30	$174.30
Purchase #2	$37.69	6.627%	$40.1877	$40.19	$40.20	$40.20
Purchase #3	$167.33	8.129%	$180.9323	$180.93	$180.95	$180.90
Purchase #4	$122.60	9.672%	$134.4579	$134.46	$134.45	$134.50
Purchase #5	$39.47	5.702%	$41.7206	$41.72	$41.70	$41.70
Purchase #6	$111.62	4.628%	$116.7858	$116.79	$116.80	$116.80
Purchase #7	$183.56	3.771%	$190.482	$190.48	$190.50	$190.50
7 purchase totals =	$829.16		$878.8879	$878.89	$878.90	$878.90