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	$12.41	10.515%	$13.7149	$13.71	$13.70	$13.70
Purchase #2	$53.72	3.165%	$55.4202	$55.42	$55.40	$55.40
Purchase #3	$10.93	10.123%	$12.0364	$12.04	$12.05	$12.00
Purchase #4	$56.83	4.798%	$59.5567	$59.56	$59.55	$59.60
Purchase #5	$82.76	4.849%	$86.773	$86.77	$86.75	$86.80
Purchase #6	$187.77	10.730%	$207.9177	$207.92	$207.90	$207.90
Purchase #7	$18.71	12.469%	$21.0429	$21.04	$21.05	$21.00
7 purchase totals =	$423.13		$456.4618	$456.46	$456.40	$456.40