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	$72.91	7.621%	$78.4665	$78.47	$78.45	$78.50
Purchase #2	$23.56	11.822%	$26.3453	$26.35	$26.35	$26.30
Purchase #3	$23.59	6.648%	$25.1583	$25.16	$25.15	$25.20
Purchase #4	$168.72	11.636%	$188.3523	$188.35	$188.35	$188.40
Purchase #5	$88.73	7.580%	$95.4557	$95.46	$95.45	$95.50
Purchase #6	$166.28	3.840%	$172.6652	$172.67	$172.65	$172.70
Purchase #7	$78.32	6.504%	$83.4139	$83.41	$83.40	$83.40
7 purchase totals =	$622.11		$669.8572	$669.87	$669.80	$670.00