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	$234.37	12.193%	$262.9467	$262.95	$262.95	$262.90
Purchase #2	$152.55	13.150%	$172.6103	$172.61	$172.60	$172.60
Purchase #3	$71.76	13.728%	$81.6112	$81.61	$81.60	$81.60
Purchase #4	$74.80	12.132%	$83.8747	$83.87	$83.85	$83.90
Purchase #5	$59.75	12.255%	$67.0724	$67.07	$67.05	$67.10
Purchase #6	$35.89	7.386%	$38.5408	$38.54	$38.55	$38.50
Purchase #7	$84.30	10.658%	$93.2847	$93.28	$93.30	$93.30
7 purchase totals =	$713.42		$799.9408	$799.93	$799.90	$799.90