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	$152.62	8.360%	$165.379	$165.38	$165.40	$165.40
Purchase #2	$92.79	11.347%	$103.3189	$103.32	$103.30	$103.30
Purchase #3	$80.63	11.727%	$90.0855	$90.09	$90.10	$90.10
Purchase #4	$62.44	12.675%	$70.3543	$70.35	$70.35	$70.40
Purchase #5	$220.77	8.132%	$238.723	$238.72	$238.70	$238.70
Purchase #6	$233.78	11.322%	$260.2486	$260.25	$260.25	$260.20
Purchase #7	$60.52	8.840%	$65.87	$65.87	$65.85	$65.90
7 purchase totals =	$903.55		$993.9793	$993.98	$993.95	$994.00