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	$98.47	7.523%	$105.8779	$105.88	$105.90	$105.90
Purchase #2	$241.66	11.499%	$269.4485	$269.45	$269.45	$269.40
Purchase #3	$136.32	4.599%	$142.5894	$142.59	$142.60	$142.60
Purchase #4	$5.80	10.719%	$6.4217	$6.42	$6.40	$6.40
Purchase #5	$33.34	7.238%	$35.7531	$35.75	$35.75	$35.80
Purchase #6	$223.48	9.703%	$245.1643	$245.16	$245.15	$245.20
Purchase #7	$122.88	6.795%	$131.2297	$131.23	$131.25	$131.20
7 purchase totals =	$861.95		$936.4846	$936.48	$936.50	$936.50