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	$129.63	6.347%	$137.8576	$137.86	$137.85	$137.90
Purchase #2	$121.54	8.478%	$131.8442	$131.84	$131.85	$131.80
Purchase #3	$9.30	10.754%	$10.3001	$10.30	$10.30	$10.30
Purchase #4	$60.45	11.747%	$67.5511	$67.55	$67.55	$67.60
Purchase #5	$122.41	11.519%	$136.5104	$136.51	$136.50	$136.50
Purchase #6	$36.73	10.525%	$40.5958	$40.60	$40.60	$40.60
Purchase #7	$133.68	8.118%	$144.5321	$144.53	$144.55	$144.50
7 purchase totals =	$613.74		$669.1913	$669.19	$669.20	$669.20