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	$92.87	7.260%	$99.6124	$99.61	$99.60	$99.60
Purchase #2	$245.50	12.212%	$275.4805	$275.48	$275.50	$275.50
Purchase #3	$149.66	9.761%	$164.2683	$164.27	$164.25	$164.30
Purchase #4	$52.71	6.780%	$56.2837	$56.28	$56.30	$56.30
Purchase #5	$180.96	9.321%	$197.8273	$197.83	$197.85	$197.80
Purchase #6	$39.74	13.165%	$44.9718	$44.97	$44.95	$45.00
Purchase #7	$91.65	9.583%	$100.4328	$100.43	$100.45	$100.40
7 purchase totals =	$853.09		$938.8768	$938.87	$938.90	$938.90