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	$224.50	3.512%	$232.3844	$232.38	$232.40	$232.40
Purchase #2	$91.88	9.459%	$100.5709	$100.57	$100.55	$100.60
Purchase #3	$213.86	8.390%	$231.8029	$231.80	$231.80	$231.80
Purchase #4	$67.54	4.195%	$70.3733	$70.37	$70.35	$70.40
Purchase #5	$111.59	11.146%	$124.0278	$124.03	$124.05	$124.00
Purchase #6	$79.85	12.495%	$89.8273	$89.83	$89.85	$89.80
Purchase #7	$236.80	6.157%	$251.3798	$251.38	$251.40	$251.40
7 purchase totals =	$1,026.02		$1,100.3664	$1,100.36	$1,100.40	$1,100.40