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	$38.60	4.211%	$40.2254	$40.23	$40.25	$40.20
Purchase #2	$247.47	4.434%	$258.4428	$258.44	$258.45	$258.40
Purchase #3	$70.35	11.195%	$78.2257	$78.23	$78.25	$78.20
Purchase #4	$151.55	12.847%	$171.0196	$171.02	$171.00	$171.00
Purchase #5	$90.47	10.442%	$99.9169	$99.92	$99.90	$99.90
Purchase #6	$243.51	7.485%	$261.7367	$261.74	$261.75	$261.70
Purchase #7	$27.94	8.336%	$30.2691	$30.27	$30.25	$30.30
7 purchase totals =	$869.89		$939.8362	$939.85	$939.85	$939.70