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	$52.31	10.688%	$57.9009	$57.90	$57.90	$57.90
Purchase #2	$204.48	11.818%	$228.6454	$228.65	$228.65	$228.60
Purchase #3	$86.46	6.156%	$91.7825	$91.78	$91.80	$91.80
Purchase #4	$127.39	9.456%	$139.436	$139.44	$139.45	$139.40
Purchase #5	$215.42	3.458%	$222.8692	$222.87	$222.85	$222.90
Purchase #6	$237.98	12.210%	$267.0374	$267.04	$267.05	$267.00
Purchase #7	$80.65	6.763%	$86.1044	$86.10	$86.10	$86.10
7 purchase totals =	$1,004.69		$1,093.7758	$1,093.78	$1,093.80	$1,093.70