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	$58.56	12.558%	$65.914	$65.91	$65.90	$65.90
Purchase #2	$49.72	12.658%	$56.0136	$56.01	$56.00	$56.00
Purchase #3	$70.35	13.516%	$79.8585	$79.86	$79.85	$79.90
Purchase #4	$125.77	13.474%	$142.7162	$142.72	$142.70	$142.70
Purchase #5	$43.42	8.146%	$46.957	$46.96	$46.95	$47.00
Purchase #6	$37.36	10.347%	$41.2256	$41.23	$41.25	$41.20
Purchase #7	$71.70	8.205%	$77.583	$77.58	$77.60	$77.60
7 purchase totals =	$456.88		$510.2679	$510.27	$510.25	$510.30