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	$145.34	3.104%	$149.8514	$149.85	$149.85	$149.90
Purchase #2	$66.40	7.779%	$71.5653	$71.57	$71.55	$71.60
Purchase #3	$217.64	6.213%	$231.162	$231.16	$231.15	$231.20
Purchase #4	$54.31	4.393%	$56.6958	$56.70	$56.70	$56.70
Purchase #5	$58.77	6.160%	$62.3902	$62.39	$62.40	$62.40
Purchase #6	$41.51	3.200%	$42.8383	$42.84	$42.85	$42.80
Purchase #7	$205.83	9.504%	$225.3921	$225.39	$225.40	$225.40
7 purchase totals =	$789.80		$839.8951	$839.90	$839.90	$840.00