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	$57.26	11.381%	$63.7768	$63.78	$63.80	$63.80
Purchase #2	$145.69	11.768%	$162.8348	$162.83	$162.85	$162.80
Purchase #3	$122.39	11.502%	$136.4673	$136.47	$136.45	$136.50
Purchase #4	$36.63	11.378%	$40.7978	$40.80	$40.80	$40.80
Purchase #5	$35.98	11.492%	$40.1148	$40.11	$40.10	$40.10
Purchase #6	$171.97	9.848%	$188.9056	$188.91	$188.90	$188.90
Purchase #7	$53.53	3.786%	$55.5566	$55.56	$55.55	$55.60
7 purchase totals =	$623.45		$688.4537	$688.46	$688.45	$688.50