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	$60.51	13.358%	$68.5929	$68.59	$68.60	$68.60
Purchase #2	$160.62	4.122%	$167.2408	$167.24	$167.25	$167.20
Purchase #3	$48.34	6.443%	$51.4545	$51.45	$51.45	$51.50
Purchase #4	$39.48	9.641%	$43.2863	$43.29	$43.30	$43.30
Purchase #5	$90.33	9.484%	$98.8969	$98.90	$98.90	$98.90
Purchase #6	$65.99	10.231%	$72.7414	$72.74	$72.75	$72.70
Purchase #7	$53.29	9.646%	$58.4304	$58.43	$58.45	$58.40
7 purchase totals =	$518.56		$560.6432	$560.64	$560.70	$560.60