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	$29.50	5.563%	$31.1411	$31.14	$31.15	$31.10
Purchase #2	$169.98	13.339%	$192.6536	$192.65	$192.65	$192.70
Purchase #3	$169.47	7.752%	$182.6073	$182.61	$182.60	$182.60
Purchase #4	$93.28	12.804%	$105.2236	$105.22	$105.20	$105.20
Purchase #5	$38.77	12.495%	$43.6143	$43.61	$43.60	$43.60
Purchase #6	$77.86	6.869%	$83.2082	$83.21	$83.20	$83.20
Purchase #7	$71.31	5.296%	$75.0866	$75.09	$75.10	$75.10
7 purchase totals =	$650.17		$713.5347	$713.53	$713.50	$713.50