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	$159.67	9.780%	$175.2857	$175.29	$175.30	$175.30
Purchase #2	$137.41	10.263%	$151.5124	$151.51	$151.50	$151.50
Purchase #3	$6.55	12.161%	$7.3465	$7.35	$7.35	$7.30
Purchase #4	$48.87	13.639%	$55.5354	$55.54	$55.55	$55.50
Purchase #5	$73.42	5.569%	$77.5088	$77.51	$77.50	$77.50
Purchase #6	$25.48	8.153%	$27.5574	$27.56	$27.55	$27.60
Purchase #7	$162.40	10.546%	$179.5267	$179.53	$179.55	$179.50
7 purchase totals =	$613.80		$674.2729	$674.29	$674.30	$674.20