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	$111.72	10.134%	$123.0417	$123.04	$123.05	$123.00
Purchase #2	$188.53	4.120%	$196.2974	$196.30	$196.30	$196.30
Purchase #3	$115.59	13.286%	$130.9473	$130.95	$130.95	$130.90
Purchase #4	$103.82	3.155%	$107.0955	$107.10	$107.10	$107.10
Purchase #5	$33.55	6.623%	$35.772	$35.77	$35.75	$35.80
Purchase #6	$228.48	9.372%	$249.8931	$249.89	$249.90	$249.90
Purchase #7	$103.76	9.438%	$113.5529	$113.55	$113.55	$113.60
7 purchase totals =	$885.45		$956.5999	$956.60	$956.60	$956.60