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	$26.52	12.186%	$29.7517	$29.75	$29.75	$29.80
Purchase #2	$240.79	12.753%	$271.4979	$271.50	$271.50	$271.50
Purchase #3	$213.55	11.836%	$238.8258	$238.83	$238.85	$238.80
Purchase #4	$41.69	4.234%	$43.4552	$43.46	$43.45	$43.50
Purchase #5	$51.73	7.171%	$55.4396	$55.44	$55.45	$55.40
Purchase #6	$159.49	4.564%	$166.7691	$166.77	$166.75	$166.80
Purchase #7	$116.86	13.506%	$132.6431	$132.64	$132.65	$132.60
7 purchase totals =	$850.63		$938.3824	$938.39	$938.40	$938.40