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	$53.30	3.639%	$55.2396	$55.24	$55.25	$55.20
Purchase #2	$232.44	9.445%	$254.394	$254.39	$254.40	$254.40
Purchase #3	$197.35	11.692%	$220.4242	$220.42	$220.40	$220.40
Purchase #4	$80.90	11.582%	$90.2698	$90.27	$90.25	$90.30
Purchase #5	$79.41	13.161%	$89.8612	$89.86	$89.85	$89.90
Purchase #6	$233.66	7.598%	$251.4135	$251.41	$251.40	$251.40
Purchase #7	$15.29	12.401%	$17.1861	$17.19	$17.20	$17.20
7 purchase totals =	$892.35		$978.7884	$978.78	$978.75	$978.80