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	$78.42	8.791%	$85.3139	$85.31	$85.30	$85.30
Purchase #2	$148.65	5.360%	$156.6176	$156.62	$156.60	$156.60
Purchase #3	$151.96	3.491%	$157.2649	$157.26	$157.25	$157.30
Purchase #4	$149.27	11.111%	$165.8554	$165.86	$165.85	$165.90
Purchase #5	$140.56	9.562%	$154.0003	$154.00	$154.00	$154.00
Purchase #6	$82.59	10.618%	$91.3594	$91.36	$91.35	$91.40
Purchase #7	$39.78	3.231%	$41.0653	$41.07	$41.05	$41.10
7 purchase totals =	$791.23		$851.4768	$851.48	$851.40	$851.60