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	$26.68	4.296%	$27.8262	$27.83	$27.85	$27.80
Purchase #2	$39.70	7.195%	$42.5564	$42.56	$42.55	$42.60
Purchase #3	$181.25	10.380%	$200.0638	$200.06	$200.05	$200.10
Purchase #4	$135.53	6.645%	$144.536	$144.54	$144.55	$144.50
Purchase #5	$117.67	9.174%	$128.465	$128.47	$128.45	$128.50
Purchase #6	$174.61	6.711%	$186.3281	$186.33	$186.35	$186.30
Purchase #7	$5.34	13.810%	$6.0775	$6.08	$6.10	$6.10
7 purchase totals =	$680.78		$735.8530	$735.87	$735.90	$735.90