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	$127.81	11.219%	$142.149	$142.15	$142.15	$142.10
Purchase #2	$158.69	5.590%	$167.5608	$167.56	$167.55	$167.60
Purchase #3	$126.36	10.180%	$139.2234	$139.22	$139.20	$139.20
Purchase #4	$29.47	12.379%	$33.1181	$33.12	$33.10	$33.10
Purchase #5	$94.56	9.106%	$103.1706	$103.17	$103.15	$103.20
Purchase #6	$62.32	12.261%	$69.9611	$69.96	$69.95	$70.00
Purchase #7	$132.96	5.368%	$140.0973	$140.10	$140.10	$140.10
7 purchase totals =	$732.17		$795.2803	$795.28	$795.20	$795.30