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	$171.94	8.383%	$186.3537	$186.35	$186.35	$186.40
Purchase #2	$55.81	4.743%	$58.4571	$58.46	$58.45	$58.50
Purchase #3	$80.47	11.184%	$89.4698	$89.47	$89.45	$89.50
Purchase #4	$57.50	11.468%	$64.0941	$64.09	$64.10	$64.10
Purchase #5	$11.73	6.347%	$12.4745	$12.47	$12.45	$12.50
Purchase #6	$19.55	7.519%	$21.02	$21.02	$21.00	$21.00
Purchase #7	$201.93	8.711%	$219.5201	$219.52	$219.50	$219.50
7 purchase totals =	$598.93		$651.3893	$651.38	$651.30	$651.50