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	$228.73	13.169%	$258.8515	$258.85	$258.85	$258.90
Purchase #2	$93.96	5.801%	$99.4106	$99.41	$99.40	$99.40
Purchase #3	$222.49	7.871%	$240.0022	$240.00	$240.00	$240.00
Purchase #4	$48.49	10.179%	$53.4258	$53.43	$53.45	$53.40
Purchase #5	$78.83	3.331%	$81.4558	$81.46	$81.45	$81.50
Purchase #6	$60.77	6.788%	$64.8951	$64.90	$64.90	$64.90
Purchase #7	$114.45	6.792%	$122.2234	$122.22	$122.20	$122.20
7 purchase totals =	$847.72		$920.2644	$920.27	$920.25	$920.30