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	$30.49	9.672%	$33.439	$33.44	$33.45	$33.40
Purchase #2	$187.59	11.452%	$209.0728	$209.07	$209.05	$209.10
Purchase #3	$20.84	3.815%	$21.635	$21.64	$21.65	$21.60
Purchase #4	$39.39	7.497%	$42.3431	$42.34	$42.35	$42.30
Purchase #5	$87.33	4.192%	$90.9909	$90.99	$91.00	$91.00
Purchase #6	$198.95	12.865%	$224.5449	$224.54	$224.55	$224.50
Purchase #7	$164.87	11.517%	$183.8581	$183.86	$183.85	$183.90
7 purchase totals =	$729.46		$805.8838	$805.88	$805.90	$805.80