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	$125.88	6.761%	$134.3907	$134.39	$134.40	$134.40
Purchase #2	$250.98	12.565%	$282.5156	$282.52	$282.50	$282.50
Purchase #3	$85.50	13.787%	$97.2879	$97.29	$97.30	$97.30
Purchase #4	$239.75	11.121%	$266.4126	$266.41	$266.40	$266.40
Purchase #5	$36.72	8.494%	$39.839	$39.84	$39.85	$39.80
Purchase #6	$141.35	10.227%	$155.8059	$155.81	$155.80	$155.80
Purchase #7	$36.54	13.855%	$41.6026	$41.60	$41.60	$41.60
7 purchase totals =	$916.72		$1,017.8543	$1,017.86	$1,017.85	$1,017.80