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	$68.96	7.202%	$73.9265	$73.93	$73.95	$73.90
Purchase #2	$90.26	10.437%	$99.6804	$99.68	$99.70	$99.70
Purchase #3	$89.31	11.471%	$99.5548	$99.55	$99.55	$99.60
Purchase #4	$71.60	12.123%	$80.2801	$80.28	$80.30	$80.30
Purchase #5	$92.46	8.176%	$100.0195	$100.02	$100.00	$100.00
Purchase #6	$42.94	4.758%	$44.9831	$44.98	$45.00	$45.00
Purchase #7	$118.36	12.688%	$133.3775	$133.38	$133.40	$133.40
7 purchase totals =	$573.89		$631.8219	$631.82	$631.90	$631.90