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	$156.57	5.671%	$165.4491	$165.45	$165.45	$165.40
Purchase #2	$64.45	9.641%	$70.6636	$70.66	$70.65	$70.70
Purchase #3	$234.65	13.267%	$265.781	$265.78	$265.80	$265.80
Purchase #4	$109.46	6.187%	$116.2323	$116.23	$116.25	$116.20
Purchase #5	$38.61	3.777%	$40.0683	$40.07	$40.05	$40.10
Purchase #6	$35.81	8.528%	$38.8639	$38.86	$38.85	$38.90
Purchase #7	$167.41	7.652%	$180.2202	$180.22	$180.20	$180.20
7 purchase totals =	$806.96		$877.2784	$877.27	$877.25	$877.30