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	$163.86	8.371%	$177.5767	$177.58	$177.60	$177.60
Purchase #2	$114.31	7.496%	$122.8787	$122.88	$122.90	$122.90
Purchase #3	$28.82	3.766%	$29.9054	$29.91	$29.90	$29.90
Purchase #4	$62.85	13.765%	$71.5013	$71.50	$71.50	$71.50
Purchase #5	$148.25	5.540%	$156.4631	$156.46	$156.45	$156.50
Purchase #6	$110.48	7.321%	$118.5682	$118.57	$118.55	$118.60
Purchase #7	$132.38	3.850%	$137.4766	$137.48	$137.50	$137.50
7 purchase totals =	$760.95		$814.3700	$814.38	$814.40	$814.50