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	$35.59	7.593%	$38.2923	$38.29	$38.30	$38.30
Purchase #2	$90.76	9.624%	$99.4947	$99.49	$99.50	$99.50
Purchase #3	$20.66	12.860%	$23.3169	$23.32	$23.30	$23.30
Purchase #4	$83.79	6.619%	$89.3361	$89.34	$89.35	$89.30
Purchase #5	$100.31	5.582%	$105.9093	$105.91	$105.90	$105.90
Purchase #6	$155.61	13.660%	$176.8663	$176.87	$176.85	$176.90
Purchase #7	$248.50	13.645%	$282.4078	$282.41	$282.40	$282.40
7 purchase totals =	$735.22		$815.6234	$815.63	$815.60	$815.60