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	$85.38	4.851%	$89.5218	$89.52	$89.50	$89.50
Purchase #2	$213.88	6.259%	$227.2667	$227.27	$227.25	$227.30
Purchase #3	$49.82	10.668%	$55.1348	$55.13	$55.15	$55.10
Purchase #4	$8.47	12.411%	$9.5212	$9.52	$9.50	$9.50
Purchase #5	$153.83	7.176%	$164.8688	$164.87	$164.85	$164.90
Purchase #6	$167.68	12.421%	$188.5075	$188.51	$188.50	$188.50
Purchase #7	$91.73	5.401%	$96.6843	$96.68	$96.70	$96.70
7 purchase totals =	$770.79		$831.5051	$831.50	$831.45	$831.50