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	$65.74	13.484%	$74.6044	$74.60	$74.60	$74.60
Purchase #2	$83.42	7.133%	$89.3703	$89.37	$89.35	$89.40
Purchase #3	$51.71	13.134%	$58.5016	$58.50	$58.50	$58.50
Purchase #4	$236.78	10.287%	$261.1376	$261.14	$261.15	$261.10
Purchase #5	$176.47	4.164%	$183.8182	$183.82	$183.80	$183.80
Purchase #6	$39.51	6.380%	$42.0307	$42.03	$42.05	$42.00
Purchase #7	$130.69	11.241%	$145.3809	$145.38	$145.40	$145.40
7 purchase totals =	$784.32		$854.8437	$854.84	$854.85	$854.80