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	$39.35	6.374%	$41.8582	$41.86	$41.85	$41.90
Purchase #2	$156.77	9.217%	$171.2195	$171.22	$171.20	$171.20
Purchase #3	$36.80	3.863%	$38.2216	$38.22	$38.20	$38.20
Purchase #4	$99.28	12.150%	$111.3425	$111.34	$111.35	$111.30
Purchase #5	$132.49	4.712%	$138.7329	$138.73	$138.75	$138.70
Purchase #6	$73.78	9.709%	$80.9433	$80.94	$80.95	$80.90
Purchase #7	$60.60	12.238%	$68.0162	$68.02	$68.00	$68.00
7 purchase totals =	$599.07		$650.3342	$650.33	$650.30	$650.20