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	$82.42	10.412%	$91.0016	$91.00	$91.00	$91.00
Purchase #2	$90.42	11.322%	$100.6574	$100.66	$100.65	$100.70
Purchase #3	$42.87	8.333%	$46.4424	$46.44	$46.45	$46.40
Purchase #4	$86.72	12.210%	$97.3085	$97.31	$97.30	$97.30
Purchase #5	$42.32	7.675%	$45.5681	$45.57	$45.55	$45.60
Purchase #6	$136.35	9.583%	$149.4164	$149.42	$149.40	$149.40
Purchase #7	$233.46	13.517%	$265.0168	$265.02	$265.00	$265.00
7 purchase totals =	$714.56		$795.4112	$795.42	$795.35	$795.40