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	$242.40	13.840%	$275.9482	$275.95	$275.95	$275.90
Purchase #2	$80.92	3.114%	$83.4398	$83.44	$83.45	$83.40
Purchase #3	$112.47	6.365%	$119.6287	$119.63	$119.65	$119.60
Purchase #4	$174.41	13.525%	$197.999	$198.00	$198.00	$198.00
Purchase #5	$220.36	3.872%	$228.8923	$228.89	$228.90	$228.90
Purchase #6	$52.90	5.296%	$55.7016	$55.70	$55.70	$55.70
Purchase #7	$118.69	7.121%	$127.1419	$127.14	$127.15	$127.10
7 purchase totals =	$1,002.15		$1,088.7515	$1,088.75	$1,088.80	$1,088.60