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	$72.32	12.440%	$81.3166	$81.32	$81.30	$81.30
Purchase #2	$182.86	8.187%	$197.8307	$197.83	$197.85	$197.80
Purchase #3	$45.94	6.267%	$48.8191	$48.82	$48.80	$48.80
Purchase #4	$92.38	10.524%	$102.1021	$102.10	$102.10	$102.10
Purchase #5	$131.46	7.653%	$141.5206	$141.52	$141.50	$141.50
Purchase #6	$9.67	5.481%	$10.2	$10.20	$10.20	$10.20
Purchase #7	$20.41	5.625%	$21.5581	$21.56	$21.55	$21.60
7 purchase totals =	$555.04		$603.3472	$603.35	$603.30	$603.30