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	$42.40	13.637%	$48.1821	$48.18	$48.20	$48.20
Purchase #2	$206.54	7.708%	$222.4601	$222.46	$222.45	$222.50
Purchase #3	$44.54	8.847%	$48.4805	$48.48	$48.50	$48.50
Purchase #4	$107.95	7.591%	$116.1445	$116.14	$116.15	$116.10
Purchase #5	$156.77	11.172%	$174.2843	$174.28	$174.30	$174.30
Purchase #6	$129.47	7.369%	$139.0106	$139.01	$139.00	$139.00
Purchase #7	$145.73	11.342%	$162.2587	$162.26	$162.25	$162.30
7 purchase totals =	$833.40		$910.8208	$910.81	$910.85	$910.90