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	$14.65	4.487%	$15.3073	$15.31	$15.30	$15.30
Purchase #2	$90.78	8.266%	$98.2839	$98.28	$98.30	$98.30
Purchase #3	$42.80	3.192%	$44.1662	$44.17	$44.15	$44.20
Purchase #4	$91.37	3.433%	$94.5067	$94.51	$94.50	$94.50
Purchase #5	$178.42	10.277%	$196.7562	$196.76	$196.75	$196.80
Purchase #6	$103.32	8.550%	$112.1539	$112.15	$112.15	$112.20
Purchase #7	$189.80	13.398%	$215.2294	$215.23	$215.25	$215.20
7 purchase totals =	$711.14		$776.4036	$776.41	$776.40	$776.50