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	$72.25	3.649%	$74.8864	$74.89	$74.90	$74.90
Purchase #2	$48.86	5.843%	$51.7149	$51.71	$51.70	$51.70
Purchase #3	$178.85	3.481%	$185.0758	$185.08	$185.10	$185.10
Purchase #4	$222.69	10.736%	$246.598	$246.60	$246.60	$246.60
Purchase #5	$65.83	5.314%	$69.3282	$69.33	$69.35	$69.30
Purchase #6	$155.83	10.140%	$171.6312	$171.63	$171.65	$171.60
Purchase #7	$84.31	8.617%	$91.575	$91.58	$91.60	$91.60
7 purchase totals =	$828.62		$890.8095	$890.82	$890.90	$890.80