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	$178.89	12.147%	$200.6198	$200.62	$200.60	$200.60
Purchase #2	$94.94	11.489%	$105.8477	$105.85	$105.85	$105.80
Purchase #3	$24.51	10.264%	$27.0257	$27.03	$27.05	$27.00
Purchase #4	$132.61	4.350%	$138.3785	$138.38	$138.40	$138.40
Purchase #5	$198.26	3.685%	$205.5659	$205.57	$205.55	$205.60
Purchase #6	$55.91	8.280%	$60.5393	$60.54	$60.55	$60.50
Purchase #7	$88.42	11.140%	$98.27	$98.27	$98.25	$98.30
7 purchase totals =	$773.54		$836.2469	$836.26	$836.25	$836.20