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	$120.42	6.410%	$128.1389	$128.14	$128.15	$128.10
Purchase #2	$70.62	8.549%	$76.6573	$76.66	$76.65	$76.70
Purchase #3	$38.43	10.620%	$42.5113	$42.51	$42.50	$42.50
Purchase #4	$35.97	12.557%	$40.4868	$40.49	$40.50	$40.50
Purchase #5	$62.99	12.771%	$71.0345	$71.03	$71.05	$71.00
Purchase #6	$226.88	4.227%	$236.4702	$236.47	$236.45	$236.50
Purchase #7	$177.66	6.699%	$189.5614	$189.56	$189.55	$189.60
7 purchase totals =	$732.97		$784.8604	$784.86	$784.85	$784.90