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	$76.70	9.396%	$83.9067	$83.91	$83.90	$83.90
Purchase #2	$64.34	13.338%	$72.9217	$72.92	$72.90	$72.90
Purchase #3	$200.54	13.208%	$227.0273	$227.03	$227.05	$227.00
Purchase #4	$61.93	4.255%	$64.5651	$64.57	$64.55	$64.60
Purchase #5	$225.78	5.713%	$238.6788	$238.68	$238.70	$238.70
Purchase #6	$80.68	11.245%	$89.7525	$89.75	$89.75	$89.80
Purchase #7	$96.30	7.777%	$103.7893	$103.79	$103.80	$103.80
7 purchase totals =	$806.27		$880.6414	$880.65	$880.65	$880.70