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	$189.51	12.616%	$213.4186	$213.42	$213.40	$213.40
Purchase #2	$132.37	3.294%	$136.7303	$136.73	$136.75	$136.70
Purchase #3	$72.57	12.773%	$81.8394	$81.84	$81.85	$81.80
Purchase #4	$159.40	13.860%	$181.4928	$181.49	$181.50	$181.50
Purchase #5	$236.52	3.608%	$245.0536	$245.05	$245.05	$245.10
Purchase #6	$169.77	5.527%	$179.1532	$179.15	$179.15	$179.20
Purchase #7	$54.95	7.746%	$59.2064	$59.21	$59.20	$59.20
7 purchase totals =	$1,015.09		$1,096.8943	$1,096.89	$1,096.90	$1,096.90