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	$21.82	7.685%	$23.4969	$23.50	$23.50	$23.50
Purchase #2	$16.88	8.574%	$18.3273	$18.33	$18.35	$18.30
Purchase #3	$131.31	7.284%	$140.8746	$140.87	$140.85	$140.90
Purchase #4	$7.41	13.169%	$8.3858	$8.39	$8.40	$8.40
Purchase #5	$35.36	11.450%	$39.4087	$39.41	$39.40	$39.40
Purchase #6	$63.89	3.181%	$65.9223	$65.92	$65.90	$65.90
Purchase #7	$65.57	3.448%	$67.8309	$67.83	$67.85	$67.80
7 purchase totals =	$342.24		$364.2465	$364.25	$364.25	$364.20