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	$86.31	3.455%	$89.292	$89.29	$89.30	$89.30
Purchase #2	$134.85	8.571%	$146.408	$146.41	$146.40	$146.40
Purchase #3	$30.87	9.308%	$33.7434	$33.74	$33.75	$33.70
Purchase #4	$179.64	4.284%	$187.3358	$187.34	$187.35	$187.30
Purchase #5	$64.97	6.345%	$69.0923	$69.09	$69.10	$69.10
Purchase #6	$75.92	3.249%	$78.3866	$78.39	$78.40	$78.40
Purchase #7	$154.60	9.431%	$169.1803	$169.18	$169.20	$169.20
7 purchase totals =	$727.16		$773.4384	$773.44	$773.50	$773.40