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	$164.98	12.397%	$185.4326	$185.43	$185.45	$185.40
Purchase #2	$36.42	6.807%	$38.8991	$38.90	$38.90	$38.90
Purchase #3	$82.93	3.153%	$85.5448	$85.54	$85.55	$85.50
Purchase #4	$193.51	12.802%	$218.2832	$218.28	$218.30	$218.30
Purchase #5	$247.40	9.240%	$270.2598	$270.26	$270.25	$270.30
Purchase #6	$73.28	6.789%	$78.255	$78.26	$78.25	$78.30
Purchase #7	$104.92	7.494%	$112.7827	$112.78	$112.80	$112.80
7 purchase totals =	$903.44		$989.4572	$989.45	$989.50	$989.50