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	$74.72	3.219%	$77.1252	$77.13	$77.15	$77.10
Purchase #2	$168.99	9.793%	$185.5392	$185.54	$185.55	$185.50
Purchase #3	$154.80	8.452%	$167.8837	$167.88	$167.90	$167.90
Purchase #4	$61.90	11.436%	$68.9789	$68.98	$69.00	$69.00
Purchase #5	$52.83	10.322%	$58.2831	$58.28	$58.30	$58.30
Purchase #6	$78.72	12.276%	$88.3837	$88.38	$88.40	$88.40
Purchase #7	$60.35	11.461%	$67.2667	$67.27	$67.25	$67.30
7 purchase totals =	$652.31		$713.4605	$713.46	$713.55	$713.50