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	$71.82	7.583%	$77.2661	$77.27	$77.25	$77.30
Purchase #2	$209.84	10.608%	$232.0998	$232.10	$232.10	$232.10
Purchase #3	$139.32	9.525%	$152.5902	$152.59	$152.60	$152.60
Purchase #4	$165.81	11.421%	$184.7472	$184.75	$184.75	$184.70
Purchase #5	$90.83	11.641%	$101.4035	$101.40	$101.40	$101.40
Purchase #6	$119.77	9.856%	$131.5745	$131.57	$131.55	$131.60
Purchase #7	$151.71	13.660%	$172.4336	$172.43	$172.45	$172.40
7 purchase totals =	$949.10		$1,052.1149	$1,052.11	$1,052.10	$1,052.10