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	$55.63	6.317%	$59.1441	$59.14	$59.15	$59.10
Purchase #2	$83.52	3.695%	$86.6061	$86.61	$86.60	$86.60
Purchase #3	$225.34	8.292%	$244.0252	$244.03	$244.05	$244.00
Purchase #4	$191.90	9.506%	$210.142	$210.14	$210.15	$210.10
Purchase #5	$42.81	13.593%	$48.6292	$48.63	$48.65	$48.60
Purchase #6	$131.60	13.110%	$148.8528	$148.85	$148.85	$148.90
Purchase #7	$174.96	11.217%	$194.5853	$194.59	$194.60	$194.60
7 purchase totals =	$905.76		$991.9847	$991.99	$992.05	$991.90