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	$159.34	11.103%	$177.0315	$177.03	$177.05	$177.00
Purchase #2	$53.64	3.610%	$55.5764	$55.58	$55.60	$55.60
Purchase #3	$156.88	11.376%	$174.7267	$174.73	$174.75	$174.70
Purchase #4	$109.39	12.651%	$123.2289	$123.23	$123.25	$123.20
Purchase #5	$131.61	12.601%	$148.1942	$148.19	$148.20	$148.20
Purchase #6	$72.66	13.737%	$82.6413	$82.64	$82.65	$82.60
Purchase #7	$91.35	8.315%	$98.9458	$98.95	$98.95	$98.90
7 purchase totals =	$774.87		$860.3448	$860.35	$860.45	$860.20