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	$215.40	3.339%	$222.5922	$222.59	$222.60	$222.60
Purchase #2	$88.33	10.434%	$97.5464	$97.55	$97.55	$97.50
Purchase #3	$246.61	10.150%	$271.6409	$271.64	$271.65	$271.60
Purchase #4	$59.32	4.326%	$61.8862	$61.89	$61.90	$61.90
Purchase #5	$82.45	8.741%	$89.657	$89.66	$89.65	$89.70
Purchase #6	$40.62	12.258%	$45.5992	$45.60	$45.60	$45.60
Purchase #7	$63.37	10.265%	$69.8749	$69.87	$69.85	$69.90
7 purchase totals =	$796.10		$858.7968	$858.80	$858.80	$858.80