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	$45.79	13.839%	$52.1269	$52.13	$52.15	$52.10
Purchase #2	$247.51	3.814%	$256.95	$256.95	$256.95	$257.00
Purchase #3	$229.61	8.362%	$248.81	$248.81	$248.80	$248.80
Purchase #4	$103.27	7.480%	$110.9946	$110.99	$111.00	$111.00
Purchase #5	$214.28	7.113%	$229.5217	$229.52	$229.50	$229.50
Purchase #6	$172.59	13.609%	$196.0778	$196.08	$196.10	$196.10
Purchase #7	$20.59	13.355%	$23.3398	$23.34	$23.35	$23.30
7 purchase totals =	$1,033.64		$1,117.8208	$1,117.82	$1,117.85	$1,117.80