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	$168.27	6.812%	$179.7326	$179.73	$179.75	$179.70
Purchase #2	$170.54	13.499%	$193.5612	$193.56	$193.55	$193.60
Purchase #3	$51.93	4.520%	$54.2772	$54.28	$54.30	$54.30
Purchase #4	$66.50	7.306%	$71.3585	$71.36	$71.35	$71.40
Purchase #5	$47.54	3.170%	$49.047	$49.05	$49.05	$49.00
Purchase #6	$50.32	4.401%	$52.5346	$52.53	$52.55	$52.50
Purchase #7	$43.29	7.244%	$46.4259	$46.43	$46.45	$46.40
7 purchase totals =	$598.39		$646.9370	$646.94	$647.00	$646.90