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	$14.72	13.523%	$16.7106	$16.71	$16.70	$16.70
Purchase #2	$109.40	4.869%	$114.7267	$114.73	$114.75	$114.70
Purchase #3	$139.78	8.408%	$151.5327	$151.53	$151.55	$151.50
Purchase #4	$25.87	9.736%	$28.3887	$28.39	$28.40	$28.40
Purchase #5	$20.63	4.425%	$21.5429	$21.54	$21.55	$21.50
Purchase #6	$27.61	12.659%	$31.1051	$31.11	$31.10	$31.10
Purchase #7	$118.57	5.268%	$124.8163	$124.82	$124.80	$124.80
7 purchase totals =	$456.58		$488.8230	$488.83	$488.85	$488.70