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	$172.93	7.490%	$185.8825	$185.88	$185.90	$185.90
Purchase #2	$154.32	5.327%	$162.5406	$162.54	$162.55	$162.50
Purchase #3	$57.82	11.698%	$64.5838	$64.58	$64.60	$64.60
Purchase #4	$74.91	11.687%	$83.6647	$83.66	$83.65	$83.70
Purchase #5	$241.34	11.703%	$269.584	$269.58	$269.60	$269.60
Purchase #6	$168.50	8.275%	$182.4434	$182.44	$182.45	$182.40
Purchase #7	$29.93	3.215%	$30.8922	$30.89	$30.90	$30.90
7 purchase totals =	$899.75		$979.5912	$979.57	$979.65	$979.60