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	$19.86	6.301%	$21.1114	$21.11	$21.10	$21.10
Purchase #2	$55.80	6.484%	$59.4181	$59.42	$59.40	$59.40
Purchase #3	$211.85	6.229%	$225.0461	$225.05	$225.05	$225.00
Purchase #4	$74.77	11.631%	$83.4665	$83.47	$83.45	$83.50
Purchase #5	$43.76	9.378%	$47.8638	$47.86	$47.85	$47.90
Purchase #6	$132.53	5.440%	$139.7396	$139.74	$139.75	$139.70
Purchase #7	$82.51	10.816%	$91.4343	$91.43	$91.45	$91.40
7 purchase totals =	$621.08		$668.0798	$668.08	$668.05	$668.00