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	$46.81	6.576%	$49.8882	$49.89	$49.90	$49.90
Purchase #2	$103.50	11.408%	$115.3073	$115.31	$115.30	$115.30
Purchase #3	$49.85	10.554%	$55.1112	$55.11	$55.10	$55.10
Purchase #4	$21.53	9.139%	$23.4976	$23.50	$23.50	$23.50
Purchase #5	$28.94	12.209%	$32.4733	$32.47	$32.45	$32.50
Purchase #6	$114.91	11.747%	$128.4085	$128.41	$128.40	$128.40
Purchase #7	$82.33	13.598%	$93.5252	$93.53	$93.55	$93.50
7 purchase totals =	$447.87		$498.2113	$498.22	$498.20	$498.20