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	$39.91	12.502%	$44.8995	$44.90	$44.90	$44.90
Purchase #2	$42.49	7.833%	$45.8182	$45.82	$45.80	$45.80
Purchase #3	$137.37	12.218%	$154.1539	$154.15	$154.15	$154.20
Purchase #4	$62.90	4.131%	$65.4984	$65.50	$65.50	$65.50
Purchase #5	$103.54	12.607%	$116.5933	$116.59	$116.60	$116.60
Purchase #6	$70.96	12.310%	$79.6952	$79.70	$79.70	$79.70
Purchase #7	$103.84	9.453%	$113.656	$113.66	$113.65	$113.70
7 purchase totals =	$561.01		$620.3145	$620.32	$620.30	$620.40