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	$14.96	4.268%	$15.5985	$15.60	$15.60	$15.60
Purchase #2	$84.30	7.304%	$90.4573	$90.46	$90.45	$90.50
Purchase #3	$135.76	12.547%	$152.7938	$152.79	$152.80	$152.80
Purchase #4	$89.27	10.407%	$98.5603	$98.56	$98.55	$98.60
Purchase #5	$17.74	10.215%	$19.5521	$19.55	$19.55	$19.60
Purchase #6	$245.99	7.510%	$264.4638	$264.46	$264.45	$264.50
Purchase #7	$126.78	12.195%	$142.2408	$142.24	$142.25	$142.20
7 purchase totals =	$714.80		$783.6666	$783.66	$783.65	$783.80