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	$96.97	12.460%	$109.0525	$109.05	$109.05	$109.10
Purchase #2	$156.51	13.199%	$177.1678	$177.17	$177.15	$177.20
Purchase #3	$24.91	10.830%	$27.6078	$27.61	$27.60	$27.60
Purchase #4	$125.25	11.415%	$139.5473	$139.55	$139.55	$139.50
Purchase #5	$66.61	4.272%	$69.4556	$69.46	$69.45	$69.50
Purchase #6	$108.52	13.348%	$123.0052	$123.01	$123.00	$123.00
Purchase #7	$40.47	13.249%	$45.8319	$45.83	$45.85	$45.80
7 purchase totals =	$619.24		$691.6681	$691.68	$691.65	$691.70