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	$42.59	6.870%	$45.5159	$45.52	$45.50	$45.50
Purchase #2	$93.88	6.748%	$100.215	$100.22	$100.20	$100.20
Purchase #3	$104.60	11.680%	$116.8173	$116.82	$116.80	$116.80
Purchase #4	$230.64	4.361%	$240.6982	$240.70	$240.70	$240.70
Purchase #5	$233.43	13.377%	$264.6559	$264.66	$264.65	$264.70
Purchase #6	$13.89	6.342%	$14.7709	$14.77	$14.75	$14.80
Purchase #7	$88.35	9.553%	$96.7901	$96.79	$96.80	$96.80
7 purchase totals =	$807.38		$879.4633	$879.48	$879.40	$879.50