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	$48.92	7.858%	$52.7641	$52.76	$52.75	$52.80
Purchase #2	$133.57	11.135%	$148.443	$148.44	$148.45	$148.40
Purchase #3	$146.68	8.332%	$158.9014	$158.90	$158.90	$158.90
Purchase #4	$58.86	4.690%	$61.6205	$61.62	$61.60	$61.60
Purchase #5	$36.96	13.745%	$42.0402	$42.04	$42.05	$42.00
Purchase #6	$222.83	12.564%	$250.8264	$250.83	$250.85	$250.80
Purchase #7	$250.83	7.705%	$270.1565	$270.16	$270.15	$270.20
7 purchase totals =	$898.65		$984.7521	$984.75	$984.75	$984.70