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	$30.30	9.380%	$33.1421	$33.14	$33.15	$33.10
Purchase #2	$32.89	9.300%	$35.9488	$35.95	$35.95	$35.90
Purchase #3	$38.49	6.706%	$41.0711	$41.07	$41.05	$41.10
Purchase #4	$174.38	7.727%	$187.8543	$187.85	$187.85	$187.90
Purchase #5	$116.34	9.476%	$127.3644	$127.36	$127.35	$127.40
Purchase #6	$128.31	11.867%	$143.5365	$143.54	$143.55	$143.50
Purchase #7	$246.28	4.872%	$258.2788	$258.28	$258.30	$258.30
7 purchase totals =	$766.99		$827.1960	$827.19	$827.20	$827.20