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	$128.27	9.458%	$140.4018	$140.40	$140.40	$140.40
Purchase #2	$60.52	13.715%	$68.8203	$68.82	$68.80	$68.80
Purchase #3	$227.63	12.222%	$255.4509	$255.45	$255.45	$255.50
Purchase #4	$136.54	5.845%	$144.5208	$144.52	$144.50	$144.50
Purchase #5	$53.92	4.195%	$56.1819	$56.18	$56.20	$56.20
Purchase #6	$80.54	11.484%	$89.7892	$89.79	$89.80	$89.80
Purchase #7	$93.95	3.423%	$97.1659	$97.17	$97.15	$97.20
7 purchase totals =	$781.37		$852.3308	$852.33	$852.30	$852.40