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	$100.25	9.307%	$109.5803	$109.58	$109.60	$109.60
Purchase #2	$215.35	13.580%	$244.5945	$244.59	$244.60	$244.60
Purchase #3	$98.99	4.663%	$103.6059	$103.61	$103.60	$103.60
Purchase #4	$141.28	4.602%	$147.7817	$147.78	$147.80	$147.80
Purchase #5	$118.82	13.511%	$134.8738	$134.87	$134.85	$134.90
Purchase #6	$47.44	11.180%	$52.7438	$52.74	$52.75	$52.70
Purchase #7	$77.28	7.288%	$82.9122	$82.91	$82.90	$82.90
7 purchase totals =	$799.41		$876.0922	$876.08	$876.10	$876.10