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	$24.91	10.119%	$27.4306	$27.43	$27.45	$27.40
Purchase #2	$92.41	12.837%	$104.2727	$104.27	$104.25	$104.30
Purchase #3	$125.86	10.419%	$138.9734	$138.97	$138.95	$139.00
Purchase #4	$61.75	9.234%	$67.452	$67.45	$67.45	$67.50
Purchase #5	$229.83	4.717%	$240.6711	$240.67	$240.65	$240.70
Purchase #6	$85.85	5.138%	$90.261	$90.26	$90.25	$90.30
Purchase #7	$86.58	6.115%	$91.8744	$91.87	$91.85	$91.90
7 purchase totals =	$707.19		$760.9352	$760.92	$760.85	$761.10