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	$248.27	12.827%	$280.1156	$280.12	$280.10	$280.10
Purchase #2	$62.49	8.235%	$67.6361	$67.64	$67.65	$67.60
Purchase #3	$161.91	10.345%	$178.6596	$178.66	$178.65	$178.70
Purchase #4	$115.53	9.618%	$126.6417	$126.64	$126.65	$126.60
Purchase #5	$206.89	13.541%	$234.905	$234.91	$234.90	$234.90
Purchase #6	$17.54	10.715%	$19.4194	$19.42	$19.40	$19.40
Purchase #7	$212.95	5.134%	$223.8829	$223.88	$223.90	$223.90
7 purchase totals =	$1,025.58		$1,131.2603	$1,131.27	$1,131.25	$1,131.20