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	$250.39	3.422%	$258.9583	$258.96	$258.95	$259.00
Purchase #2	$90.79	3.709%	$94.1574	$94.16	$94.15	$94.20
Purchase #3	$236.92	4.432%	$247.4203	$247.42	$247.40	$247.40
Purchase #4	$29.66	11.835%	$33.1703	$33.17	$33.15	$33.20
Purchase #5	$86.92	4.561%	$90.8844	$90.88	$90.90	$90.90
Purchase #6	$71.92	3.777%	$74.6364	$74.64	$74.65	$74.60
Purchase #7	$235.33	12.164%	$263.9555	$263.96	$263.95	$264.00
7 purchase totals =	$1,001.93		$1,063.1826	$1,063.19	$1,063.15	$1,063.30