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	$68.97	13.551%	$78.3161	$78.32	$78.30	$78.30
Purchase #2	$246.98	11.712%	$275.9063	$275.91	$275.90	$275.90
Purchase #3	$16.59	13.488%	$18.8277	$18.83	$18.85	$18.80
Purchase #4	$37.26	11.466%	$41.5322	$41.53	$41.55	$41.50
Purchase #5	$28.53	6.715%	$30.4458	$30.45	$30.45	$30.40
Purchase #6	$37.70	10.463%	$41.6446	$41.64	$41.65	$41.60
Purchase #7	$221.89	5.474%	$234.0363	$234.04	$234.05	$234.00
7 purchase totals =	$657.92		$720.7090	$720.72	$720.75	$720.50