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	$49.74	4.850%	$52.1524	$52.15	$52.15	$52.20
Purchase #2	$18.95	13.154%	$21.4427	$21.44	$21.45	$21.40
Purchase #3	$34.64	12.170%	$38.8557	$38.86	$38.85	$38.90
Purchase #4	$171.46	9.756%	$188.1876	$188.19	$188.20	$188.20
Purchase #5	$90.87	13.164%	$102.8321	$102.83	$102.85	$102.80
Purchase #6	$56.34	6.266%	$59.8703	$59.87	$59.85	$59.90
Purchase #7	$82.77	6.532%	$88.1765	$88.18	$88.20	$88.20
7 purchase totals =	$504.77		$551.5173	$551.52	$551.55	$551.60