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	$225.69	13.709%	$256.6298	$256.63	$256.65	$256.60
Purchase #2	$27.61	13.748%	$31.4058	$31.41	$31.40	$31.40
Purchase #3	$34.97	9.172%	$38.1774	$38.18	$38.20	$38.20
Purchase #4	$164.62	6.692%	$175.6364	$175.64	$175.65	$175.60
Purchase #5	$130.25	9.269%	$142.3229	$142.32	$142.30	$142.30
Purchase #6	$124.90	10.275%	$137.7335	$137.73	$137.75	$137.70
Purchase #7	$123.68	12.703%	$139.3911	$139.39	$139.40	$139.40
7 purchase totals =	$831.72		$921.2969	$921.30	$921.35	$921.20