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	$199.32	9.602%	$218.4587	$218.46	$218.45	$218.50
Purchase #2	$86.85	8.423%	$94.1654	$94.17	$94.15	$94.20
Purchase #3	$36.45	11.183%	$40.5262	$40.53	$40.55	$40.50
Purchase #4	$120.88	9.147%	$131.9369	$131.94	$131.95	$131.90
Purchase #5	$35.27	10.826%	$39.0883	$39.09	$39.10	$39.10
Purchase #6	$57.47	4.668%	$60.1527	$60.15	$60.15	$60.20
Purchase #7	$243.61	6.637%	$259.7784	$259.78	$259.80	$259.80
7 purchase totals =	$779.85		$844.1066	$844.12	$844.15	$844.20