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	$159.28	9.821%	$174.9229	$174.92	$174.90	$174.90
Purchase #2	$144.25	8.816%	$156.9671	$156.97	$156.95	$157.00
Purchase #3	$60.54	6.798%	$64.6555	$64.66	$64.65	$64.70
Purchase #4	$78.91	4.125%	$82.165	$82.17	$82.15	$82.20
Purchase #5	$12.65	12.818%	$14.2715	$14.27	$14.25	$14.30
Purchase #6	$133.32	12.775%	$150.3516	$150.35	$150.35	$150.40
Purchase #7	$148.38	5.548%	$156.6121	$156.61	$156.60	$156.60
7 purchase totals =	$737.33		$799.9457	$799.95	$799.85	$800.10