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	$76.49	9.711%	$83.9179	$83.92	$83.90	$83.90
Purchase #2	$182.58	8.781%	$198.6123	$198.61	$198.60	$198.60
Purchase #3	$104.59	11.304%	$116.4129	$116.41	$116.40	$116.40
Purchase #4	$112.38	13.309%	$127.3367	$127.34	$127.35	$127.30
Purchase #5	$156.57	7.258%	$167.9339	$167.93	$167.95	$167.90
Purchase #6	$241.54	9.328%	$264.0709	$264.07	$264.05	$264.10
Purchase #7	$210.59	13.322%	$238.6448	$238.64	$238.65	$238.60
7 purchase totals =	$1,084.74		$1,196.9294	$1,196.92	$1,196.90	$1,196.80