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	$13.88	10.669%	$15.3609	$15.36	$15.35	$15.40
Purchase #2	$248.26	13.272%	$281.2091	$281.21	$281.20	$281.20
Purchase #3	$90.90	13.649%	$103.3069	$103.31	$103.30	$103.30
Purchase #4	$108.73	13.583%	$123.4988	$123.50	$123.50	$123.50
Purchase #5	$160.27	4.370%	$167.2738	$167.27	$167.25	$167.30
Purchase #6	$27.52	9.556%	$30.1498	$30.15	$30.15	$30.10
Purchase #7	$88.61	7.647%	$95.386	$95.39	$95.40	$95.40
7 purchase totals =	$738.17		$816.1853	$816.19	$816.15	$816.20