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	$29.70	4.430%	$31.0157	$31.02	$31.00	$31.00
Purchase #2	$114.35	11.391%	$127.3756	$127.38	$127.40	$127.40
Purchase #3	$19.33	13.275%	$21.8961	$21.90	$21.90	$21.90
Purchase #4	$34.97	11.622%	$39.0342	$39.03	$39.05	$39.00
Purchase #5	$28.42	13.676%	$32.3067	$32.31	$32.30	$32.30
Purchase #6	$94.42	9.863%	$103.7326	$103.73	$103.75	$103.70
Purchase #7	$237.87	5.504%	$250.9624	$250.96	$250.95	$251.00
7 purchase totals =	$559.06		$606.3233	$606.33	$606.35	$606.30