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	$46.93	9.486%	$51.3818	$51.38	$51.40	$51.40
Purchase #2	$168.25	11.505%	$187.6072	$187.61	$187.60	$187.60
Purchase #3	$231.86	10.780%	$256.8545	$256.85	$256.85	$256.90
Purchase #4	$67.98	9.637%	$74.5312	$74.53	$74.55	$74.50
Purchase #5	$135.98	9.273%	$148.5894	$148.59	$148.60	$148.60
Purchase #6	$51.68	11.318%	$57.5291	$57.53	$57.55	$57.50
Purchase #7	$42.94	4.540%	$44.8895	$44.89	$44.90	$44.90
7 purchase totals =	$745.62		$821.3827	$821.38	$821.45	$821.40