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	$72.84	3.506%	$75.3938	$75.39	$75.40	$75.40
Purchase #2	$91.35	8.859%	$99.4427	$99.44	$99.45	$99.40
Purchase #3	$72.32	11.267%	$80.4683	$80.47	$80.45	$80.50
Purchase #4	$150.51	3.489%	$155.7613	$155.76	$155.75	$155.80
Purchase #5	$211.97	7.370%	$227.5922	$227.59	$227.60	$227.60
Purchase #6	$97.90	11.627%	$109.2828	$109.28	$109.30	$109.30
Purchase #7	$81.83	5.215%	$86.0974	$86.10	$86.10	$86.10
7 purchase totals =	$778.72		$834.0385	$834.03	$834.05	$834.10