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	$38.55	9.824%	$42.3372	$42.34	$42.35	$42.30
Purchase #2	$141.54	10.859%	$156.9098	$156.91	$156.90	$156.90
Purchase #3	$124.33	10.716%	$137.6532	$137.65	$137.65	$137.70
Purchase #4	$20.66	3.602%	$21.4042	$21.40	$21.40	$21.40
Purchase #5	$74.55	8.293%	$80.7324	$80.73	$80.75	$80.70
Purchase #6	$92.27	11.498%	$102.8792	$102.88	$102.90	$102.90
Purchase #7	$46.84	13.677%	$53.2463	$53.25	$53.25	$53.20
7 purchase totals =	$538.74		$595.1623	$595.16	$595.20	$595.10