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	$84.85	6.857%	$90.6682	$90.67	$90.65	$90.70
Purchase #2	$217.47	9.229%	$237.5403	$237.54	$237.55	$237.50
Purchase #3	$73.87	9.276%	$80.7222	$80.72	$80.70	$80.70
Purchase #4	$94.55	12.740%	$106.5957	$106.60	$106.60	$106.60
Purchase #5	$122.68	13.814%	$139.627	$139.63	$139.65	$139.60
Purchase #6	$110.96	5.340%	$116.8853	$116.89	$116.90	$116.90
Purchase #7	$54.90	11.211%	$61.0548	$61.05	$61.05	$61.10
7 purchase totals =	$759.28		$833.0935	$833.10	$833.10	$833.10