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	$66.36	9.704%	$72.7996	$72.80	$72.80	$72.80
Purchase #2	$14.56	3.270%	$15.0361	$15.04	$15.05	$15.00
Purchase #3	$34.90	5.823%	$36.9322	$36.93	$36.95	$36.90
Purchase #4	$138.50	10.145%	$152.5508	$152.55	$152.55	$152.60
Purchase #5	$25.89	11.775%	$28.9385	$28.94	$28.95	$28.90
Purchase #6	$163.33	13.574%	$185.5004	$185.50	$185.50	$185.50
Purchase #7	$48.37	6.223%	$51.3801	$51.38	$51.40	$51.40
7 purchase totals =	$491.91		$543.1377	$543.14	$543.20	$543.10