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	$132.66	6.157%	$140.8279	$140.83	$140.85	$140.80
Purchase #2	$41.37	9.609%	$45.3452	$45.35	$45.35	$45.30
Purchase #3	$38.34	5.662%	$40.5108	$40.51	$40.50	$40.50
Purchase #4	$81.95	10.246%	$90.3466	$90.35	$90.35	$90.30
Purchase #5	$139.87	8.488%	$151.7422	$151.74	$151.75	$151.70
Purchase #6	$235.27	3.344%	$243.1374	$243.14	$243.15	$243.10
Purchase #7	$138.77	5.163%	$145.9347	$145.93	$145.95	$145.90
7 purchase totals =	$808.23		$857.8448	$857.85	$857.90	$857.60