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	$51.89	12.694%	$58.4769	$58.48	$58.50	$58.50
Purchase #2	$164.66	13.835%	$187.4407	$187.44	$187.45	$187.40
Purchase #3	$119.75	11.448%	$133.459	$133.46	$133.45	$133.50
Purchase #4	$115.88	11.201%	$128.8597	$128.86	$128.85	$128.90
Purchase #5	$158.87	3.302%	$164.1159	$164.12	$164.10	$164.10
Purchase #6	$39.83	9.381%	$43.5665	$43.57	$43.55	$43.60
Purchase #7	$200.35	9.287%	$218.9565	$218.96	$218.95	$219.00
7 purchase totals =	$851.23		$934.8752	$934.89	$934.85	$935.00