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	$101.96	9.789%	$111.9409	$111.94	$111.95	$111.90
Purchase #2	$106.92	6.629%	$114.0077	$114.01	$114.00	$114.00
Purchase #3	$63.99	12.584%	$72.0425	$72.04	$72.05	$72.00
Purchase #4	$119.54	4.148%	$124.4985	$124.50	$124.50	$124.50
Purchase #5	$72.49	10.769%	$80.2964	$80.30	$80.30	$80.30
Purchase #6	$135.52	5.370%	$142.7974	$142.80	$142.80	$142.80
Purchase #7	$168.45	3.163%	$173.7781	$173.78	$173.80	$173.80
7 purchase totals =	$768.87		$819.3615	$819.37	$819.40	$819.30