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	$52.89	8.568%	$57.4216	$57.42	$57.40	$57.40
Purchase #2	$90.85	12.746%	$102.4297	$102.43	$102.45	$102.40
Purchase #3	$239.38	12.215%	$268.6203	$268.62	$268.60	$268.60
Purchase #4	$93.88	10.820%	$104.0378	$104.04	$104.05	$104.00
Purchase #5	$117.51	12.137%	$131.7722	$131.77	$131.75	$131.80
Purchase #6	$55.39	10.814%	$61.3799	$61.38	$61.40	$61.40
Purchase #7	$70.38	4.481%	$73.5337	$73.53	$73.55	$73.50
7 purchase totals =	$720.28		$799.1952	$799.19	$799.20	$799.10