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	$72.75	6.169%	$77.2379	$77.24	$77.25	$77.20
Purchase #2	$129.72	12.726%	$146.2282	$146.23	$146.25	$146.20
Purchase #3	$10.68	10.326%	$11.7828	$11.78	$11.80	$11.80
Purchase #4	$98.80	11.190%	$109.8557	$109.86	$109.85	$109.90
Purchase #5	$39.39	10.820%	$43.652	$43.65	$43.65	$43.70
Purchase #6	$171.56	11.171%	$190.725	$190.73	$190.75	$190.70
Purchase #7	$163.82	4.710%	$171.5359	$171.54	$171.55	$171.50
7 purchase totals =	$686.72		$751.0175	$751.03	$751.10	$751.00