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	$142.38	12.264%	$159.8415	$159.84	$159.85	$159.80
Purchase #2	$94.61	5.130%	$99.4635	$99.46	$99.45	$99.50
Purchase #3	$93.84	6.487%	$99.9274	$99.93	$99.95	$99.90
Purchase #4	$127.98	6.219%	$135.9391	$135.94	$135.95	$135.90
Purchase #5	$74.29	12.789%	$83.7909	$83.79	$83.80	$83.80
Purchase #6	$101.60	3.410%	$105.0646	$105.06	$105.05	$105.10
Purchase #7	$204.79	5.119%	$215.2732	$215.27	$215.25	$215.30
7 purchase totals =	$839.49		$899.3002	$899.29	$899.30	$899.30