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	$36.40	6.760%	$38.8606	$38.86	$38.85	$38.90
Purchase #2	$175.33	11.150%	$194.8793	$194.88	$194.90	$194.90
Purchase #3	$137.79	13.275%	$156.0816	$156.08	$156.10	$156.10
Purchase #4	$49.34	4.298%	$51.4606	$51.46	$51.45	$51.50
Purchase #5	$79.95	13.322%	$90.6009	$90.60	$90.60	$90.60
Purchase #6	$79.82	10.427%	$88.1428	$88.14	$88.15	$88.10
Purchase #7	$227.84	13.654%	$258.9493	$258.95	$258.95	$258.90
7 purchase totals =	$786.47		$878.9751	$878.97	$879.00	$879.00