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	$66.64	8.534%	$72.3271	$72.33	$72.35	$72.30
Purchase #2	$127.75	12.647%	$143.9065	$143.91	$143.90	$143.90
Purchase #3	$92.38	7.504%	$99.3122	$99.31	$99.30	$99.30
Purchase #4	$128.98	5.179%	$135.6599	$135.66	$135.65	$135.70
Purchase #5	$96.93	5.141%	$101.9132	$101.91	$101.90	$101.90
Purchase #6	$47.60	8.277%	$51.5399	$51.54	$51.55	$51.50
Purchase #7	$235.88	6.640%	$251.5424	$251.54	$251.55	$251.50
7 purchase totals =	$796.16		$856.2012	$856.20	$856.20	$856.10