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	$247.62	13.162%	$280.2117	$280.21	$280.20	$280.20
Purchase #2	$215.76	9.590%	$236.4514	$236.45	$236.45	$236.50
Purchase #3	$67.45	9.461%	$73.8314	$73.83	$73.85	$73.80
Purchase #4	$78.93	13.119%	$89.2848	$89.28	$89.30	$89.30
Purchase #5	$144.39	5.845%	$152.8296	$152.83	$152.85	$152.80
Purchase #6	$36.57	12.371%	$41.0941	$41.09	$41.10	$41.10
Purchase #7	$129.42	7.608%	$139.2663	$139.27	$139.25	$139.30
7 purchase totals =	$920.14		$1,012.9693	$1,012.96	$1,013.00	$1,013.00