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	$82.55	8.412%	$89.4941	$89.49	$89.50	$89.50
Purchase #2	$20.46	11.285%	$22.7689	$22.77	$22.75	$22.80
Purchase #3	$115.93	9.161%	$126.5503	$126.55	$126.55	$126.60
Purchase #4	$47.54	4.241%	$49.5562	$49.56	$49.55	$49.60
Purchase #5	$73.36	12.297%	$82.3811	$82.38	$82.40	$82.40
Purchase #6	$16.65	10.824%	$18.4522	$18.45	$18.45	$18.50
Purchase #7	$52.79	12.435%	$59.3544	$59.35	$59.35	$59.40
7 purchase totals =	$409.28		$448.5572	$448.55	$448.55	$448.80