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	$54.36	6.507%	$57.8972	$57.90	$57.90	$57.90
Purchase #2	$87.63	3.275%	$90.4999	$90.50	$90.50	$90.50
Purchase #3	$214.85	3.143%	$221.6027	$221.60	$221.60	$221.60
Purchase #4	$89.65	11.189%	$99.6809	$99.68	$99.70	$99.70
Purchase #5	$57.41	13.709%	$65.2803	$65.28	$65.30	$65.30
Purchase #6	$46.51	8.787%	$50.5968	$50.60	$50.60	$50.60
Purchase #7	$192.93	3.770%	$200.2035	$200.20	$200.20	$200.20
7 purchase totals =	$743.34		$785.7613	$785.76	$785.80	$785.80