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	$243.63	9.520%	$266.8236	$266.82	$266.80	$266.80
Purchase #2	$133.98	12.645%	$150.9218	$150.92	$150.90	$150.90
Purchase #3	$156.95	7.311%	$168.4246	$168.42	$168.40	$168.40
Purchase #4	$10.95	8.312%	$11.8602	$11.86	$11.85	$11.90
Purchase #5	$60.30	11.218%	$67.0645	$67.06	$67.05	$67.10
Purchase #6	$80.25	11.472%	$89.4563	$89.46	$89.45	$89.50
Purchase #7	$216.82	4.797%	$227.2209	$227.22	$227.20	$227.20
7 purchase totals =	$902.88		$981.7719	$981.76	$981.65	$981.80