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	$11.37	13.607%	$12.9171	$12.92	$12.90	$12.90
Purchase #2	$219.64	9.169%	$239.7788	$239.78	$239.80	$239.80
Purchase #3	$166.59	10.498%	$184.0786	$184.08	$184.10	$184.10
Purchase #4	$171.97	7.313%	$184.5462	$184.55	$184.55	$184.50
Purchase #5	$177.47	6.385%	$188.8015	$188.80	$188.80	$188.80
Purchase #6	$85.72	5.367%	$90.3206	$90.32	$90.30	$90.30
Purchase #7	$45.82	10.247%	$50.5152	$50.52	$50.50	$50.50
7 purchase totals =	$878.58		$950.9580	$950.97	$950.95	$950.90