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	$44.50	9.216%	$48.6011	$48.60	$48.60	$48.60
Purchase #2	$150.37	6.142%	$159.6057	$159.61	$159.60	$159.60
Purchase #3	$198.66	4.687%	$207.9712	$207.97	$207.95	$208.00
Purchase #4	$180.63	5.592%	$190.7308	$190.73	$190.75	$190.70
Purchase #5	$69.42	13.556%	$78.8306	$78.83	$78.85	$78.80
Purchase #6	$179.78	3.383%	$185.862	$185.86	$185.85	$185.90
Purchase #7	$37.48	9.123%	$40.8993	$40.90	$40.90	$40.90
7 purchase totals =	$860.84		$912.5007	$912.50	$912.50	$912.50