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	$151.49	5.137%	$159.272	$159.27	$159.25	$159.30
Purchase #2	$121.81	7.567%	$131.0274	$131.03	$131.05	$131.00
Purchase #3	$66.89	13.874%	$76.1703	$76.17	$76.15	$76.20
Purchase #4	$163.54	5.503%	$172.5396	$172.54	$172.55	$172.50
Purchase #5	$156.49	3.799%	$162.4351	$162.44	$162.45	$162.40
Purchase #6	$24.64	12.152%	$27.6343	$27.63	$27.65	$27.60
Purchase #7	$65.29	13.232%	$73.9292	$73.93	$73.95	$73.90
7 purchase totals =	$750.15		$803.0079	$803.01	$803.05	$802.90