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	$78.40	3.464%	$81.1158	$81.12	$81.10	$81.10
Purchase #2	$136.55	11.722%	$152.5564	$152.56	$152.55	$152.60
Purchase #3	$71.57	12.729%	$80.6801	$80.68	$80.70	$80.70
Purchase #4	$160.68	12.301%	$180.4452	$180.45	$180.45	$180.40
Purchase #5	$80.90	4.399%	$84.4588	$84.46	$84.45	$84.50
Purchase #6	$133.54	11.493%	$148.8878	$148.89	$148.90	$148.90
Purchase #7	$103.60	12.351%	$116.3956	$116.40	$116.40	$116.40
7 purchase totals =	$765.24		$844.5397	$844.56	$844.55	$844.60