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	$27.40	7.806%	$29.5388	$29.54	$29.55	$29.50
Purchase #2	$109.38	9.552%	$119.828	$119.83	$119.85	$119.80
Purchase #3	$102.51	8.553%	$111.2777	$111.28	$111.30	$111.30
Purchase #4	$133.77	4.503%	$139.7937	$139.79	$139.80	$139.80
Purchase #5	$169.82	10.853%	$188.2506	$188.25	$188.25	$188.30
Purchase #6	$218.92	11.732%	$244.6037	$244.60	$244.60	$244.60
Purchase #7	$243.86	12.260%	$273.7572	$273.76	$273.75	$273.80
7 purchase totals =	$1,005.66		$1,107.0497	$1,107.05	$1,107.10	$1,107.10