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	$242.43	5.749%	$256.3673	$256.37	$256.35	$256.40
Purchase #2	$244.79	13.754%	$278.4584	$278.46	$278.45	$278.50
Purchase #3	$206.30	10.669%	$228.3101	$228.31	$228.30	$228.30
Purchase #4	$82.46	3.635%	$85.4574	$85.46	$85.45	$85.50
Purchase #5	$25.94	12.516%	$29.1867	$29.19	$29.20	$29.20
Purchase #6	$68.33	4.573%	$71.4547	$71.45	$71.45	$71.50
Purchase #7	$184.56	6.621%	$196.7797	$196.78	$196.80	$196.80
7 purchase totals =	$1,054.81		$1,146.0143	$1,146.02	$1,146.00	$1,146.20