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	$247.73	13.399%	$280.9233	$280.92	$280.90	$280.90
Purchase #2	$160.25	5.801%	$169.5461	$169.55	$169.55	$169.50
Purchase #3	$118.65	7.129%	$127.1086	$127.11	$127.10	$127.10
Purchase #4	$203.37	12.108%	$227.994	$227.99	$228.00	$228.00
Purchase #5	$154.68	9.186%	$168.8889	$168.89	$168.90	$168.90
Purchase #6	$44.58	11.182%	$49.5649	$49.56	$49.55	$49.60
Purchase #7	$111.48	10.867%	$123.5945	$123.59	$123.60	$123.60
7 purchase totals =	$1,040.74		$1,147.6203	$1,147.61	$1,147.60	$1,147.60